I remember reading somebodys post on here saying that when they swapped engines, they had to go to their local state police barraks with their truck (along with the old engine) and they were able to give the dude the paperwork he needed to go to the DMV to get a title with the "new" VIN number (the number stamped in the engine).
My guess is that even back in the 40's they knew that those "Mfg By" plates held on with two pop rivits were easy to swap around, so thats why alot of states chose to use the number on the block instead.
As far as those "Mfg By General Motors Corp" plates are concerned.. i've seen repros available on eBay and other sources that were blank in the seriel number spot.. so you could stamp your own number in there.. pretty handy for restorations.
