302's are sort of hard to find, look just like 228, 236, 248, 256, 270, SN stamped on machined surface on right side of block by starter, start w/ displacement, i. e. 302xxxx. Some smaller, earlier, (non-270/302)engines have small bellhousing that won't take large(11")clutch. Adapter plate available to use modern bellhousing that is much easier to R & R(InlinersInternational.org). Two 'Good' heads(larger valves, ports), two 'average' heads; casting nos. tell diff, both come on 270/302's. All heads not interchangeable w/ all pistons. Patrick's in AZ has 9:1 pistons, lots of other parts, good catalogue w/ casting nos. Good luck.

'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.