Before you think about changing the engine, it might be well to get it inspected using a VIN found somewhere on the frame, otherwise, any title tied to the engine ser. no. will be invalid. In CO, however, they only honor an inspection for 3 years, but it doesn't say that on the official form. One can get a title only, no registration, no license plate, to solve that problem.

'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.