Hey guys! new member here and first time diesel owner. I picked up this K20 tonight and drove it 5 hours home, the frame and body are like new, but the engine is another story. since its 2:27am I'll just post quick little bullets about what was happening.
Also the truck is a 1983 Chevy K20 with a 6.2, it has the SM465 and the head gaskets,intake gaskets, and valve seals were recently redone i was told. Anywho the problems on my trip i experienced was:
- Misfire [ truck seemed to be running okay when i first got it, but as the night went on the miss got worse.]

- Rattling/knocking [when the truck is under load it will have a random clatter/knock come out of no where, its loud enough to make me jump every time plus the truck speeds up for a second, it only does this when theres a heavy load on the engine plus the truck pours black smoke every time this happens. and the whole thing only lasts for about a split second. and its never consistant it just pops out of no where.]

- Getting hot [ The truck seemed that when ever i would hit a hill the temperature would like to climb fast but it never went over 220 useually stayed at 195 on the flat.]

- oil PSI [ i didnt exactly pay attention to this on the 5 hour drive home but the oil psi gradually dropped from 50 to 25 and then when i got in my yard and left it idle for a second i noticed it was on zero.. but the truck wasnt knocking or anything. ]

-Sparks from drivers tail pipe?! [ My friend who was following me home said that occasionally a bunch of sparks would shoot out the drivers side pipe. ]

and the previous owner pretty much left me hanging dry when i called him back about it, didnt want nothing to do with it anymore and the famous saying "oh it never did that to me before."
Anywho, if anyone knows what my problems are that'd be great. My dad has another 6.2 diesel sitting around if i need it, but i dont exactly want to start changing engines on a truck i just bought... plus i also have a 355 Gas engine thats built up some, kinda debating on what to do here.

 

I'd be having a look at your turbo.

 

I am thinking the truck is Non turbo as he is saying sparks are coming from the driver side tail pipe I have a 84 NA 6.2 and they came factory with dual exhaust regardless sparks do not sound good,To answer the question as to doing a gas swap to it I would not do it because anything a 355 will do a 6.2 with a turbo will do better including way better fuel mileage.

 

no turbo, and the 6.2 told me what was happening by ceasing solid today. turns out the rear main seal let go, and the runaway was oil getting up into the combustion chamber. so I'll be putting a new engine in it. at least the truck is in really good shape, so atleast thats a positive.
http://s996.photobucket.com/user/kurama49/media/IMG_1760_zps46e2d4eb.jpg.html

 

If you decide that you are gonna turbo it get big block engine mounts for clearance for the crossover pipe.