Jerry, welcome to Stovebolt land. You're in good company here. While a GMC is technically not a Stovebolt, it's close enough...
The 270 was GMC's base pickup engine from the late 50's thru early 60's when it was retired. Prior to that it saw extensive military use in the Korean war era. A real workhorse of a motor, Full pressure crank (no babbit dippers ever for GMC) very sturdy and reliable, some parts interchange with Chev 235 but many parts are proprietary. A little on the expensive side to rebuild.
WWW.inliners.org is a good site to learn more on the 270 Jimmy.
You should be looking for major rust damage on the '55 as this will be the most labor-intensive and expensive part of the restoration(if that's indeed what you are planning) Check the floorboards and cab corners. Otherwise just look it over like you would any vehicle and be honest with yourself about what you are getting into.
If the truck is driveable, evaluate it like you would any used car. Chevy had two totally different 1/2 tons in '55, the "1st series" and the actual 55. I think GMC did too but not sure. Look for leaking fluids, missing trim (some GMC pieces can be hard to find - unlike Chevy), operation of clutch, tranmission etc. If the motor smokes, knocks or has other bad signs, see above - GMC's are not cheap to rebuild.
I'm sure some others will add to this but be sure to visit Rob English's web site. It is the absolute best resource on the web for GMC info. go to
www.oldgmctrucks.com.
