3/4- 1 ton frames

[GM72K10]

Can you check the vin on the frame? Its on the frame rail above the bed on the 81 and up, see pic. Not sure about 80 and back. The vin on the cab should be on the door post. And the vin on the frame on the 81-87 trucks wouldn't give you the model number, just the last digits of the serial number. A 1 ton 4x4 77-80 should be CK#3@& Where the first digit is C for Chevy T for GMC, 2nd digit K for four wheel drive, 3rd digit is a Letter Code for engine type, 4th digit would be a 3 for 30 series (1 ton), 5th digit a 3 if a chassis Cab or a 4 for a pickup, 6 th digit is for year. Hope some of this helps.

So a CKL348Jxxxxxx would be a 78 K30 pickup with a 350. The vin decode info is available on the internet. Good Luck.