[WyattTX]

You will make the purists cringe, but it can be made to work. 81-87, and 73-80 are very different cosmetically on the inside and out. You will also need to take the guage cluster out of the '81 truck too, because the 73-80 gauge bezel wont fit it. The tailgate on the '81 will look much different than a '73, but still work. Your end result will basically be an '81 with a '73 front clip. Perhaps you could take the drive train out of your '73, and put it in the '81, So you dont have to do as much mix, and match work. This would be the easiest route, without ending up with too much of a Frankenstein truck. Good luck.