whoa! you bought a truck from a guy who ran it into a tree??!! and then took a different truck with a title that didn't belong to it?? and you don't even know what company made the truck??
A - talk to CA DMV about it, but you better have the story straight about the vin# on the title AND the truck first
B - spend some time reading the forums here, looking at the gallery here, and find some info
here ... the serial number just tells you what you already know, but there's some info
here, including a vin decoder
C - parts for the 3/4T will be scarcer then for 1/2T, and GMC specific parts will be scarcer than for the same year/model Chevy
Bill