Dranoff said approvals for the project were at "the 3-yard line," with Councilman Mark Squilla set to introduce legislation in City Council to extend the zoning designation CMX-5, which allows a higher building floor area in relation to the lot, past Spruce Street to Pine Street.
"That is how we sized our building," Dranoff said.
Neighborhood meetings resulted in changes to the design, he said, adding that "Kohn attended every one of them."
The plans include separate lobbies for the SLS hotel and residences; street-level stores; a corner bar and restaurant; and a 6,000-square-foot, double-height glass ballroom on the fifth floor, overlooking the Kimmel.
The hotel's 149 rooms will occupy floors eight through 17, with 13 rooms on each. The 18th floor will have six hotel suites.
The 125 residential units - one-, two- and three-bedroom condos and two penthouses - will begin on the 19th floor. There will be four levels of parking, one underground and three above-grade, for 220 spaces shared by residents and hotel guests.
In interviews, Dranoff and Kohn, whose local credits include the Four Seasons Hotel on Logan Square and the BNY Mellon Center, called the project "a game-changer" for Philadelphia.
Speaking from Paris, Kohn said, "Carl was the first one to care about South Broad Street."
The project "is as much a key to the city's growth as the Four Seasons was to the area west of Broad Street. It will become a catalyst for future development," said Kohn, who said he considers this his legacy to the city.
A graduate of Central High School and the University of Pennsylvania, Kohn also designed the international terminal at Philadelphia International Airport.
"Great cities build great buildings," said Dranoff, who has built Symphony House and 777 South Broad Street, and is building Southstar Lofts at South Street, on the Avenue of the Arts.
"I look at the Avenue of the Arts as a progression," he said. "Its development as a center for culture and the performing arts set the table for me."
Originally, the 25,000-square-foot hotel/condo site in the 300 block of South Broad - acquired by Dranoff last summer after several years - was three parcels, one owned by the University of the Arts and the others by Kenny Gamble and Philadelphia International Records.
The building will be called SLS International, Dranoff said, partly because of the SLS hotel but also "to pay homage to the home and studios of Philadelphia International Records and the rich musical history that unfolded there."
The studios and offices at 309 S. Broad where Gamble and Leon Huff produced many of their 170 gold records was severely damaged by arson in February 2010.
"The fire was a tipping point" for the record company, said Dranoff, who has worked with Gamble on other Avenue of the Arts projects.
Both 309 and 311 S. Broad, which will be demolished, are vacant. (The latter building is structurally impaired and is being stabilized by interior struts.) The University of the Arts site at 313 S. Broad, which had a pop-up garden last summer, has been cleared.
SLS Hotels is part of SBE founder Sam Nazarian's growing global empire. It has hotels open or under construction in Los Angeles, Miami, Las Vegas, and New York, as well as in China.
In an interview from Los Angeles, Nazarian said his decision to come to Philadelphia was motivated by the "opportunity to partner with a developer who understands cities."
Such projects "reinvigorate core urban areas, [where] people want to live, be entertained, and celebrate life events," he said. "We don't run our hotels simply as nightclubs with rooms, but as timeless and consistent communities, embracing a level of service and luxury that define where people want to live."
"Philadelphia is already committed to creativity through the Avenue of the Arts, and this project will elevate it," said Nazarian, whose nephew attends the Wharton School, "and we like going to places where we can help neighborhoods transform over the next 10 to 20 years."
Dranoff declined to give a price range for the condos. He said that the success of 10 Rittenhouse Square, the luxury high-rise on South 18th Street that has nearly sold out since the lender iStar brought him in, first as receiver, in 2011, motivated him to launch what will be his most expensive project.
The last units at 10 Rittenhouse were commanding $1,050 a square foot.
"Both SBE and I have a lot of skin in the game, but financing is in the wings, and we are fully committed to building this project," Dranoff said.
Kohn said it was the "dream of every architect to go back home to do something special," and the SLS International will let him do so. His late mother would be more than pleased, he said.
"Whenever I was doing a project in Philadelphia, she was always so happy," Kohn said. "She made sure everyone knew about it."