REAL ESTATE

Zell Group Calls for Modified Bid: A group led by Chicago investor Sam Zell proposed modifying its bid for control of Rockefeller Center to let existing shareholders retain a bigger stake. First, of its proposed $250-million investment, Zell has offered to let existing shareholders put in $100 million by buying new shares of stock. The new proposal also calls for the Zell group to offer Goldman Sachs’ Whitehall Street investment fund $30 million to let it buy out the debt Whitehall holds in the mortgage holder. Zell’s announcement came just two days after Rockefeller Center Properties Inc., the mortgage holder, said it would consider two new offers for the New York landmark, which has been mired in bankruptcy since May 11.