Quote
how can the frames be the same if the wheelbase is 10" longer?


I think the wheel base is different because the extracab from 89-95 is longer than the extracab of the 84-88.
I'm not sure if the frame legnth is different or not though.
It may be.
Many people have put 89-95 beds on the 84-88 frames, and they line up perfectly except for the last bolt (about 1/2" off from what I've heard).
Todd

1986 Pickup extracab longbed "Woody edition"
SAS - 33's, 5.29's, lockright rear.

02 IS300 SportCross - my "DD"
94 2wd v6 extracab
04 Outback Wagon- wife's/family car