If your 1953 GMC is a 3/4-ton, then it is a 150, not a 3600, as GMC's series/model number system is also different than Chevrolet's. A GMC 1/2-ton is 100, 3/4-ton is 150, 1-ton is 250, etc.
The Canadian GM truck numbering system from that time period makes more sense than the US system... sorry, I digress.
As far as your VIN / Title goes, you may be in for some trouble since the VIN you gave is an Engine Number and the truck no longer has that engine... Many of us on this board have been done that road, and it's really no fun at all. Hopefully you can get that resolved without much blood shed. Each state handles that situation differently, and it may as simple as a form or affidavit completed by the seller explaining why the vin on the truck does not match the title. Engine swaps are very common and sometimes the paper trail breaks down. Good luck. If this is not your problem/question, then sorry for troubling the waters.
Your best source for sound, correct, legal info about this is your state's auto licensing agency/ DMV.
