The 87 Avanti had a transition in Brake Boosters/MC's. There were cars that use the same booster as the 73 - 85. Somewhere in the production run, they were changed to the more updated GM canted style. Old Style The booster from a 1973 AMC Matador 304 CID engine was a exact fit for an 87 Avanti. The part number was cardone 503107. I believe it is the same one used at least from 1973 to 1987 Avanti's as my 73 is the same. New type My '87 Avanti uses the same dual-diaphragm booster as a '87 Monte Carlo or El Camino. Cardone Industries # 54-71243 Most auto stores will carry Cardone. Examples Good luck, Jim Wood