Is it a long bed or short bed? I agree with 69 GMC, rare is a funny word. I just removed the big block from my '72 suburban to put an LS motor in. Didn't bother me too much as the suburban is a driver, not completely stock, and a 3/4 ton. Most 3/4 tons that I have seen have big blocks. How far are you wanting to customize the truck. The truck might be worth more to some in its original state if you are going crazy custom, however if your just wanting to change out the motor I wouldn't stress about it too much. Although there is something to be said about customizing a completely stock vehicle in good condition, sometimes makes it an easier process (just ask N2Trux). Now if it is a short bed, then we have an entirely different situation. But as said before,
And welcome to the board!
Shawn