Baby John,
I recently installed a new rear mounted fuel tank on my 72 C10. I used the fuel tank out of a 69 Camaro. I did the drop down license plate and it works great. I used the filler tube and grommet from the original tank to finish it out. I have included a link to a recently post - along the same lines, we took the original fuel tank (behind the seat) and made a speaker box out of it and it bolted up perfectly. Please PM if you have additional questions.
http://67-72chevytrucks.com/vboard/s...d.php?t=522264
Good Luck,
KellerMac