From what I understand, there were trucks with title numbers taken from the VIN plate, and trucks with title numbers taken from the engine.. sounds like you have one of those taken from the VIN plate.
Now if the numbers on your VIN plate match the title, i'd leave sleeping dogs lie, since the garden variety DMV person isn't going to know that the ribs on the firewall are from a 48, not a 49.
What likely happened was a person had a solid body but no title (like a old barn find or junkyard score) and they had a shot body with a title, so they just did the ole switch-a-roo.
Laws vary from state to state, but i'd be willing to bet that the "ole switch-a-roo" when it comes to VIN numbers/plates is a big no-no.. mostly because they want you to:
A: Pay sales tax on both vehicles
B: Make sure you are the legal owner of both vehicles (i.e. not using a good title and VIN plate on a stolen truck)
Now if you're 100% sure that the truck is legit, then i'd let it ride.. but god help you if one day you're tooling down the road and somebody says, "HEY! Thats my truck!!"
If there are no other identifying numbers on the truck, I really don't know how you'd go about researching it any further as far as the history.. i suppose you could try and trace the title you have back thru previous owners (undoubetedly over many years) and then try and track those people down to ask them (provided their last known address isn't a cemetary).
