I think your tag is not original either. Check with your local DMV as stated. They will have a solution for you. If you bought this on ebay, they may also have a solution with their guarantee if the time line is not past. Put your body tag number
HERE Double check before you go to the DMV.
There will not be a vin number stamped on the frame for this year. As stated your truck was registered with the original engine, this was common practice by many DMV'S.
Your tag should be attached with either clutch head screws or philip head screws. replacement tags are available from vendors such as
Jim Carter