No, they are not the same. They appear on ebay rather freequently. Also look up
www.oldgmctrucks.com. There are many knowledgeable folks over there who love gmc trucks and there engine. Lastly try putting an add in the parts wated section.
John
PS a 53 GMC 1/2 ton would have a designation of 100, where a chebby would have the 3100 designitaion.