As Correy said, Automatics don't have a flywheel so you'll need to find one. and when you get it, the flywheel and specifically its CPS tone ring must match your 89 or your truck won't run. The tone ring on a 96 will be different.
if the clutch assembly comes with the release bearing, then grab the 96. but either year clutch will work. I'm running the original 88 clutch with my swapped-in 99 AX-15.
not sure on the pedal assembly. :dunno:
the later model clutch master cylinder can be made to bolt to the older truck, but it takes a bit of fab work. someone here had a write up on that, but I don't remember if it ever got into the DIY forum so it might be in the Tech forum. :hmm:
Get the 96 bellhousing. :thumbsup: it will be external slave and superior to the older ones.