I'm going to sum up what you've got, just to be sure its all right.
You have a 78 truck with a dead auto trans. You have your choice of a manual trans from a 76 (hydro clutch) or one setup for a cable clutch from a 78 or newer.
Sounds like you are on the right track, go with the trans setup for the cable clutch. The coversion for a 78 to run a hydro clutch setup is ugly. You have to swap the pedal hanger and cut a hole in the firewall in exactly the right place to mount the master cylinder. So here is the parts list you'll need to convert, as I recall it at least:
Clutch pedal
Brake pedal (auto trans has the fat pedal, gets in way of clutch)
Clutch cable assembly
Trans that is setup for cable clutch (fork comes out driver's side)
Shifter boot
Driveline (might have to check this, but on my 77 the yoke spline count was different)
Flywheel
Clutch and pressure plate
There are some wiring things to mess with, but none of it is absolutely vital to making it go. The reverse lights should wire up without trouble, but the auto trans carb won't have all the hookups for the coasting richer system as I recall.
I recommend keeping the console from the auto shifter. Not the whole thing, but the plastic that goes over it. You need to bend a bit of sheetmetal into a bracket to hold up the part towards the firewall, just use the auto shifter as a model. Without it, you see the ragged ends of the carpet where it was cut out for the auto shifter to sit. It looks pretty nice with the console there, and you get to keep the cubby hole for tossing change into.
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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)
MEPR: Man, my 4x4 makes all other LUVs look good
