The 270 in mine is a '58 or '59 based on the casting number. Its been some years since I looked at that. And mine is 12-volt.
Aftermarket support for the GMC inlines is out there, but its not as strong as for the Chevy inlines and nothing like what you see for the small block Chevy or Ford motors.
The decision to go GMC inline will mean spending more money and making less power than choosing to go 350 Chevy. You need to know that and be comfortable with it before you start. I'm building a '54 GMC 1-ton and decided to go V-8 because I wanted more power. I chose a Cadillac 500 so I'm still dealing with limited and expensive after-market support.
There is an ATHS show in late August every year just a few miles north of you at Brooks. I missed last year but the year before I saw a couple of GMC motors for sale in the swap meet portion.
James Larrowe lives in Sandy (east of Portland) and deals in GMC parts and likely has a motor or two available. He is likely to have used performance parts available too.
If you are going to build a GMC motor you will want to join the forum at OldGMCTrucks.com. You'll find a number of guys there who have built 270 and 302 GMCs for 'high performance' street use. Mine is just a stocker.
