If the price was right, I'd be on it like a hobo on a ham sandwich.
No disrespect to hobos or ham were meant in the comment above.
Me and Tinkerbell appriciate that.
Some people take lots of truck bits and build a truck.
My guess, as others have said, is the title came with another truck that might have met an untimely death, and it either got plates from that dead truck, or the truck was sold to the current owner with the 1978 title. Or the owner and DMV just pulled something together when it was 'reconstructed'.
GMC M135 and M211 trucks did not have 2 speed axles or transfer cases, as the low gearing was in the transmission itself. If they are still both GMC axles, then it pretty much HAS to have an original GMC transfer, as it has two propeller drives out the back to get to both axles. Unless it has a CCKW transfer and transmission, which was also a popular transplant in the M211 series, especialy if they got repowered.
Either way, it is a hodge podge and could work great together or be a rusty can with a lot of loose bolts in it.
Looking forward to the pics and write ups after you take a peek at it.