The best block "to start with" is the one you can find that is not cracked or otherwise damaged. Use the "Casting #'s" link on this page to see the numbers that identify 302 blocks. "Military" blocks may be somewhat more readily available. They require an electric fuel pump and some grinding on the passenger side of block so a starter can be installed.
Some "late" 302s were produced with a "small-port" head; you will likely want the earlier head with larger (1.75-inch) ports. A large-port 270-H head will bolt to the 302 block, but will require pistons different from those used with the 302 head.
The 302's great strength is low- and mid-range torque. My "streetable" 320 cid 302 ran in at 265 hp at 4390 rpm and 362 ft-lbs of torque at 3065 rpm. i think that the GMC can be made to run with any engine of its time--the 1950s--in a full-bodied automobile. Gearing and weight and other factors will enter into that equation. If you plan to run above 5000 rpm, you should have the best vibration damper you can afford.
As the brother says, these engines are expensive to build. Do not skimp on the machine work or the assembly.
If you seek now to replicate what could have been done in the 1950s, the 302 is an excellent inline choice, and few of its competitors in that time can match it. If you want to make the most power and rpm that you can make with an inline, then the later Chevrolet 292 or the Ford 300 are wiser choices--but they will always be more expensive than a modern "crate motor" and will be hard put to make more power.
God's Peace to you.
d
Inliner #1450
