Ok to make a long story short, I've got my Grand Pas 86 XLT 5.0efi AOD it's been running bad (don't drive it much) but I just sold my other truck so I'm going to be driving this one a lot until spring at least.
I've only got 60psi compression on #7.
I just bought a parts truck (actually for body parts) that is an 86, 4.9 with the carb feedback system and C6 trans.
The parts truck is in REALLY good cond but has frame rust in back (ok to drive but wouldn't want to pull a trailer or work it hard). I bought it cheap because the owner just bought it, tinkered with it and wouldn't start back. When I switched to the other fuel tank it started and I drove it on the trailer lol).
I've been around Pas old truck for years, it's always missed or stumbled and to be quite honest I'm kinda sick of the 5.0 and not much into rebuilding it, especially now that I have a smooth running 300 parked 20ft away.
The other hand is the parts truck is almost too nice to butcher, the body / paint / int etc are in great cond (for a 30yr old truck) and the int is beigh (I need red for Pa's truck).
If I can make up my mind on what to do, and decide to butcher the parts truck and put the 300 in instead of the 5.0 (this is what I'm leaning toward btw), as long as I swap computers, the rest of the harness / body connectors appear to be the same. Since both are 86 is it a fairly straight forward swap? I know the mtr mounts, etc, it's primarily the electrical I'm concerned with.
Not sure how much it'll matter but I'm dropping the AOD for a 4spd manual also (from a 3rd 86 truck that had a 4.9). I've got all the clutch, pedals, cylinders, cross member, etc, etc, just can't see if there are provisions in the AOD body for the shifter and cylinder mounting.

Any advice or tips are greatly appreciated. I've got the radiators from all 3 trucks btw.

Going to be a busy weekend, but as of right now I'm officially "truck less" unless I want to drive the 5.0 that misses like crap.

 

With all the parts trucks you have, it should be fairly easy to make whatever you want out of one of them. With the computer controls and all of the stuff you run into making a swap, having a complete parts truck is the only way to go.

I had an 86 F150 with the 302V8 and a C6 transmission for a while. The only issue I had with it was that the ignition module was mounted on the distributor right behind the radiator and on a hot summer day with the AC on, the module would overheat to the point the engine would miss under load. This is a generic problem on those.

 

Thanks Roadie, I thought this was the case, but I hate to pull 2 engines and a trans, then install an engine, trans, pedals, etc just to find out something wont work lol

 

Your best move is to replace the frame in Pa's truck, and keep it stock. Then find & fix the engine problem. It should be relatively easy - the 5.0L is typically a smooth-running engine, and its problems are well-known by now.

You'll run into several issues putting the 300ci into the V8 truck that will be a lot of work for no benefit - with NONE of those problems, you could just drive the I6 truck.

I'd start by doing a full compression test on the 5.0L as described in the caption of this chart:



Then continue with these:

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