Did your truck come factory with the 3 speed? The reason I changed...is I've had 2 A500s in the truck and the OD.went out on both. I know they weren't fresh rebuilds, but I bought a low mileage 87 3.9 and 3 speed when a lifter keeper broke and wore a lobe off the Cam in the 88 model 3.9. So I had the transmission and I converted it over.
So what gear does your truck have in here.it?
What kind of motor/trans config. Had the 3:21 gearing underneath?3.23 wasn't an offered size for 1988.
3.21 was, though.
And $1200 isn't bad; you may pay that much getting a rear end into snuff to run.
(What's wrong with the one in the 87 parts truck?)