Thanks a lot folks for your answers. I am a new comer (You may have already figured out by now)on this field so I would try to have some rational answers for you:
BIGGY.-GMC 54 Pick up half ton. no idea reagrding engine size.
HEDGEHOG.-The smoke comes from the GMC 54, just recently purchased after being sited for at least eight years. Smoke came out when I started after those eight years. I changed oil previously. After some time running, about 20 minutes the engine died after a fowl. I could not restart it.
POPCORN.- It has already a fowler on every spark plug.
If in need of rings/ seals, where can I get them?
FRANK54.- GMC54 currently has Champion J18C, no idea on the others. Somebody also told me to use Autolite 333 or so. I may use AC44 or 46 as per your comment. What may be be a hotter number?.
OLDCARKOOK.- Thanks a lot for the manual copies, it solves some of my current questions. I will spend some time reading it.

Chevy'51
GMC '54
GMC '56
GMC '59