I think the 89-90 4cyl 5spd is the v5m21 designation, which is just another name for the KM145.

The v4aw2 is the hydro 4spd a/t. The v4aw3 is electronic shift. Don't know if the v4aw3 is larger.

KM148/v4aw2's have removable bellhousings. To put a v6 a/t into a 2.6, you just swap the BH, and use the 4cy torque converter. Note that some km148's have lockup tc's, but not the 87-somewhere in 89 models. You have to use the right converter with the right tranny...

Not responsible for advice not taken...