engine running rough and smokine

[edszuk]

Hello all, I just picked up a lone bed 65 for my son. The engine runs but blows lots of black smoke and runs really crappy. It's going to be his first vehicle and figured him and I can work on it, but didn't want to put alot of money into it right away. I would like to keep the straight six in, but will have to come up with something else if I have to rebuild it. I do have a buick V6 3.8 with an automatic trans that I could put in it the truck but don't know if I have to modify the motor mounts.

So, the straight six cranks right up, sort of idles blows black smoke and sort of pops.
Suggestions?

Thanks,
Ed