It's actually efi. 85 was the first year it was an option. Although it has been swapped.

 

Sorry to say it has been several years since I rebuild an engine, Headers the problem is removing the old manifolds without breaking the bolts/studs (most headers are set up to match the engine and truck) then rebuild/replace the exhaust system from the header back. There are two schools of thought on exhaust installation welding and clamping both work it is your choice I prefer clamping (don't own a welder)

Hope this helps

 

Cams are supposedly pretty easily done on these trucks although I've never done one myself.

Most people complain about headers for numerous reasons. For starters removing the manifold bolts/studs typically means one or more break and then you end up having to remove the head. Some people says multiple sprays of PB blaster per day over 3 days or so will work, I'm not so sure and I'm waiting to remove those until next year. Next, depending on the headers you purchase and your exact undercarriage setup, a lot of times crossmembers have to be cut or the headers modified. Because of that, I've got 4x4, I decided to never upgrade the headers.

You can go to a 4 barrel carb with the stock setup if you get an adapter plate, but if you want to leave the rest of that stuff stock, just stick with a 2 barrel carb...I never understood the logic of getting a 4 barrel carb when all you're going to do is adapt it to a 2 barrel intake.