How difficult is it to restore a truck?

I have a 1980 something GMC sierra rusting away in the back yard. It belonged to my dad and he says it is "locked up." How difficult would it be to restore this truck to working order and possibly drop a 454 in it? I have never done a restoration project before but i have done plenty repair work to implements, trucks and tractors on the farm so I am not new to the tool box. Body work isn't my main concern right now i would just like to get the truck running for now.