(FORTUNE Magazine) – Right now the most luxurious and powerful vehicle made by Chrysler Corp. is the Gulfstream IV jet. But soon the honor will revert to a much slower machine, the new Lamborghini Diablo. That's because Lee A. Iacocca is ( divesting the aerospace and defense outfits he picked up in a diversification campaign begun five years ago. Chrysler, the smallest and most vulnerable of the Big Three, will focus instead on protecting its core business now that auto sales have shifted into low gear. To potential buyers, the real prize in the sell-off will be Gulfstream Aerospace, the Savannah-based planemaker. Gulfstream Chairman Allen Paulson, 67, is bidding to buy back the company. He initially purchased Gulfstream from Grumman for $52 million in 1978, and set out to turn around what was then a money-losing outfit. He pocketed $85 million by taking Gulfstream public in 1983 and collected over $400 million by selling to Chrysler in 1985. To avoid any appearance of conflict of interest, Paulson, a former TWA mechanic who signs birthday cards for each of Gulfstream's 5,500 employees, is taking a leave of absence until the company is sold. If he regains ownership, he will devote considerable time to a pet project: a supersonic business jet that would carry 12 passengers and travel 2,000 mph (550 mph faster than the Concorde). Gulfstream is in ''concept development'' on the mini-SST, along with Britain's Rolls-Royce. Another partner is the Soviet Union's Sukhoi design bureau -- the folks who created the Su-17 fighter. If the $1 billion project flies, Paulson may need lessons in Cyrillic to keep track of the birthdays of his Russian comrades.