Good Evening,
Lets start by saying NICE TRUCK !!! The GMC guys covered your options on the 228 and 270. 302's are great engines, I've only seen one. I'm not a fan of the v-8 conversions, and not sure what you would gain. Basically, more horsepower and not enough brakes to stop it. A tuned stovebolt is highly dependable.
As for the rims - those 18" splits are three piece rims, not widow makers. One can only find tube tires for them and they can be expensive. The alternatives are the 19.5's mentioned above with a tubeless 8R-19.5 tire. These are the only rims that would fit over the big one-ton rear drums. And by the way, don't ever let your 1-ton brake parts out of your sight. Shoes are not available and must be relined, and the drums are not available anywhere after market.
Don't let anyone talk you into surfacing the drums. You need all the metal you could get for a long time.
That rear "pumpkin" can be swapped out from the 5:xx differential to a more friendly 4:10 or 4:11. Everything else is available and mostly identical to the 1/2 tons and 3/4 tons. Kingpins come to mind as a bit larger, as well as the wheel cylinders. Brake springs between the shoes are out there but you must do a bit of research.
Good luck, and we hope to hear more from you on the "BOLT"
Joe
