1986.5 Supra

Look for a 87' to 89'. i know that they didnt change much to the car in those years.  I had a friend that had one.  The stereo harness was cut, it was a pita to find the right wires.  Basically find the same color wires, and those would be the 4 speaker pos and neg connections.  To find out if they are front or rear, get a battery; like a AA and tap then connection, this will "pop" the speaker. Then get a test light to find the switched and the current wires, then the power antenna should be blue.

If you look for a 89 to 93 car, the back pods can be moded to fit 6.5 speakers, i think all around. Otherwise, with some fabing 4 in components can be fit all around in that stock car.