The 89 turbo head is different, I never thought if this would also be true in a normally aspirated application. Visually the 89 Turbo head has massive exhaust guide extension down into the port. This could be in an 88 head also. I did not research for any other differences.

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.