Originally Posted by jorb
This website deals specifically with GMC trucks.
http://www.oldgmctrucks.com/

They have a Discussion Board that you can join.

I'm not sure but your truck should of had a number emblem on the side of the hood above or below the GMC emblem.
Something like 100, 150, 350 would give you the model/series tonnage of the the truck.

The tag on the drives side hinge pillar should give you the year/model/series of the truck.

oldgmctrucks.com website is kind of hard to find stuff but just keep clicking on links and you will eventually find more info..
ID page
http://www.oldgmctrucks.com/page0012.html

GMC Serial number page
http://www.oldgmctrucks.com/page0010.html

281 22 = series 280
http://www.oldgmctrucks.com/page0015.html

That website, and those pages, are what I used to decode his truck at the beginning of this post. I declared it a 1T because it is what the documents/website say it is. Mr. Rob English lists the page that includes 280 series as 1/2, 3/4, 1T. I think it was assumed all 1 1/2 T, and up, were on the next page. The rest of the internet seems to say that a 280 series is a 1.5T as Mike and the lug nuts say.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn