Auto to Manual Swap - 1st Gen

Just find another 89-93 4.3 5 speed and take everything you need off it. It's a fairly big project. I'd pull the seats, dash and steering column for starters. I think the crossmember will be OK. Not sure on the driveshaft. You'll need to do some re-wiring to eliminate the park neutral safety switch and add the clutch safety switch. Back ups are wired different also. A 91 S10 factory service manual and this wiring manual would be a big help:
This is a 1990 S10 Factory manual, but IIRC there should be no differences:

There won't be any cable to the pedal it's all hydraulic. You rear end is fine as is. It's based more on engine size than trans type.
Do a search on here for auto to manual swaps. I get the feeling you need to study the details bit more before tearing into your truck.

If it's a 4.3, some had 3.08 rear ends and got better mileage than the more common 3.42 which had worse mpg, but better acceleration. Particularly in the heavier models.