Hey Beltran1988, Early Classic Ent. had an article write up on just this type of mod. on just this model of truck. http://www.earlyclassic.com/tech.asp...20No!-Shortbed It gives info on where to cut and how much to cut, this is something I plan on having to do myself because finding a decent shortbed 60-66 GMC truck in the Vegas area is getting tough.
Good luck, Tony.