90-92 MkIII had a different crossmember that was used to fit the 1JZ in. It fits both the 7M and the 1JZ, but the 86.5-"89.4" had one that only fits the 7M, since the M engine had been around since 1965 but the JZ was introduced in 89.

I believe thats also when they swapped over to the 7M crank (cylinders 2 and 5 had counterweights on them and as such lowered the redline to 6250 RPM from the 6500 RPM that the 86.5-88s had) as well as liquid engine mounts.

The front end, mirrors, taillights, wastegate actuator, temp gauge, trim, etc. had also been changed. The "firewall badge" that told the transmission, paint code, and differential was moved to the door jam as well. I think the seats were slightly different. The steering wheel was awesome instead of ghey too