IT took the Macklowes three weeks of intense round-the-clock due diligence to pull together their purchase of eight premier office buildings from Blackstone.

Speaking at the Young Mens’/Womens’ Real Estate Association luncheon yesterday, William S. “Billy” Macklowe said when he and his father, Harry, heard Blackstone would have to increase its offer for Equity Office Properties, they realized the private-equity giant would have to sell off assets.

That’s when they reached out to take them on, the younger Macklowe said.

“The whole thing was done on a handshake,” he said. “If they won, we won.”

Deutsche Bank provided financing for the $7 billion used to buy 6.5 million feet worth of Class A towers, including Worldwide Plaza, 1301 Sixth Ave. and Tower 56 at 126 E. 56th St.

Meanwhile, as we first reported last year, Macklowe Properties has turned 510 Madison Ave. into a 30-story, 350,000-foot office building.

It will be laid out similarly to the Lever House, with column-free 10,000-foot upper floors and a base of 17,000 feet. A health club with pool and garden terrace – kept up with water collected from the roof – will create a transitional setback on the sixth floor.

CB Richard Ellis is the agent, led by Mary Ann Tighe and Paul Amrich, who told us rents will be over $100 a foot but balked at providing specifics on the rents of the top floors.

As for the Drake Hotel site, Macklowe said, “Dad and I are still evaluating that from a residential perspective, a commercial perspective, a retail element and hotel. The plan we have with the Drake right now is to conclude our demolition.”

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In another family deal, Stanley Wasserman and sons Alan and Mark just paid $130.5 million for an apartment building in Gramercy Park at 245 E. 19th St. that will remain a rental.

Constructed by Punia and Marx in 1958, the sprawling apartments have huge alcoves and lots of space – but still rent for an average of $19 a foot in a market that commands $50.

Originally built on leased land, descendants of the founders, the Punia and Marx families – Jeffrey Punia, Laurie Zucker and Elizabeth “Betty” Crane – have over the years bought back about half of the land under the building.

The sellers were able to buy all of the land once broker Brian Ezratty of Eastern Consolidated Properties was hired, which helped spur a bidding war involving 13 parties that finally ended this month with the Wasserman deal.

“[The Wassermans] have been doing this a long time and they put up a strong deposit and said they wanted to own it,” said Ezratty, who noted about five groups were bundled in the same price range.

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Luxury menswear purveyor Thomas Pink is signed, sealed and delivered at 63 Wall St., also known as The Crest.

The retailer inked a 10-year pact with Nathan Berman‘s Metro Loft Management for just shy of 4,000 feet, settling into the same block where BMW holds court.

Michael Hofmann of Colliers ABR brought in the tenant to the building, which was represented by Darrell Rubens of Winick Realty Group.

“The space they took was the former headquarters of Brown Brothers,” Rubens said. The asking rent was $200 a foot and they are expected to open over the summer.

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