For years, Mayor Thomas M. Menino stood as the biggest hurdle in Don Chiofaro's quest to build two skyscrapers where his Boston Harbor Garage now stands.
Chiofaro has found a more receptive audience in City Hall with Menino's successor: Mayor Martin J. Walsh wants to see a bold development replace the aging concrete bunker now on the site.
Some degree of public opposition persists, along with questions about the size and scope of the project. But there are also signs of movement — a willingness to compromise, a sense of inevitability that something new should be built.
In coming weeks, the Boston Redevelopment Authority will offer its recommendations for development on the waterfront area that stretches from the Marriott Long Wharf hotel to the Hook Lobster property. Among the expected details: new size parameters for the garage parcel and nearby properties.
Richard McGuinness, deputy director for waterfront planning at the BRA, said Walsh is eager to get rid of the garage and to see an exciting project take its place. He said the BRA intends to allow for some variations in the project's design.
"I think we would consider an exception for height here for an exceptional building," McGuinness said. "We want to make sure our build-out allowance is flexible enough that something good could occur there, whether it's now or sometime in the future."
The most recent plan, which Chiofaro made public last year, called for two towers, one 600 feet high and the other more than 530 feet. He wants a mixed-use project with a total of 1.3 million square feet of office, residential, and other uses.
But McGuinness isn't saying whether the city would allow such a dramatic request.
Height won't be the only challenge. The BRA will look at density, analyzing the proposed project's footprint and its impacts on shadows, wind, and harbor views.
Chiofaro will also need to make the case for why the civic uses and amenities he has proposed — his plan for a central common area protected from the elements with a retractable glass roof, for example — are strong enough to allow him to bypass strict state regulations on waterfront buildings.
The height limit unveiled by the BRA in coming weeks will probably be more than the 200 feet that Menino stuck to, citing guidelines for that part of the Rose Fitzgerald Kennedy Greenway, but less than the roughly 600 foot limit imposed by the Federal Aviation Administration.
McGuinness said Chiofaro has also floated an alternative to the two-tower plan, one that would include all 1.3 million square feet in a single tower, roughly 600 feet high, that might not cast as many shadows across that part of the city.
But big obstacles remain.
The developer has shown no willingness to budge on the project's total size, and he faces a delicate dance with his wary neighbors — the two Harbor Towers condo buildings on one side and the New England Aquarium on another — as he appeals to Walsh for support.
The potential for one or two towers at that site has loomed since Chiofaro and equity partner Prudential Real Estate Investors acquired the 1,400-space garage for more than $150 million in 2007.
Chiofaro, perhaps best known for his International Place towers nearby, made it clear at the time that he wanted to tear down the garage and replace it with a massive, mixed-use project. But when he bought into the garage property, he also bought into a tangle with residents of the 400-foot Harbor Towers complex next door.
Marcelle Willock, a retired doctor who lives in Harbor Towers, said she and many of her neighbors believe the new complex should complement the skyline, not mar it. Yet she said she's eager to see the garage redeveloped.
"We live in the 21st century and . . . understand that tall buildings have got to be built," Willock said. "But we'd also like to see a building of some architectural significance, and not just another box put up there."
There are other concerns. Harbor Towers residents maintain a lease for a portion of the parking in the garage, as well as a long-term lease for a huge boiler housed on the garage property. Chiofaro will need to ensure both parking and heating continue uninterrupted.
Lee Kozol, chairman of the Harbor Towers owners' garage committee, said the biggest frustration is the potential for an outsized project, one that would draw too many cars and delivery trucks to an already congested Atlantic Avenue or drastically hurt the waterfront views.
"Everything is excessively sized," Kozol said of Chiofaro's plans. "We feel that it would simply be overwhelming for the area."
New England Aquarium officials want reassurances that water and power lines won't be severed during construction and that vibrations, dust, and noise from the work won't affect the sea creatures.
Eric Krauss, the aquarium's chief operating officer, said he wants to make sure the 1.4 million people who visit the attraction every year can get past the construction unimpeded — and find parking once the garage is torn down. Redevelopment could help revitalize that part of the waterfront, he said, but aquarium officials are waiting for more details from Chiofaro.
Don Chiofaro Jr., a project manager who works with his father at Chiofaro Co., said the developer is still working on possible solutions for interim parking during construction. The goal would be to replace the 1,400 spaces in the garage with underground parking in the new project.
So far, the younger Chiofaro said, the 1.3 million-square-foot size is necessary to make the redevelopment financially feasible.
"The garage is extremely valuable as is," Don Chiofaro Jr. said. "And it's incredibly costly to rebuild that structure [underground]."
While initiated on Menino's watch, the process of planning the next phase of development along that area of the waterfront has largely taken place over the last year and a half, during the Walsh administration. Don Chiofaro Jr. said he has been measuring the progress by the age of his twins: They were born just after the planning started, and now they're 20 months old.
Still, Chiofaro Jr. sounded more hopeful than antagonistic — a dramatic switch from the famously contentious relationship his father had with Menino.
"Certainly, the current administration has been more receptive to tall buildings, across the board, across the city," he said. "[And] the administration of the BRA has been much more open-minded to the concepts we have there."
Jon Chesto can be reached at email@example.com. Follow him on Twitter @jonchesto.