Cool! Let me know if your coming through Yuma, and i'd be happy to show you the M211. Lots of places in AZ to go vehicle hunting, especially MV's. There's a guy here in my small home town that is selling a CHERRY completely original untouched M715 Jeep.
Back to the motor question. The poop is I currently have the 455 Olds in my M220 torn apart because I found severe pitting in the cylinder walls. The cost of a complete rebuild is going to be basically the same as looking for an entirely different motor, which has definately crossed my mind. I would LOVE to throw a diesel in it for the simplicity, sound, smell and option of running waste veggie oil which is still cheap here. I don't have the funds for anything other than a small GM diesel and from the reading i've done the 6.2 would fit the bill nicely. It won't be a powerhouse, but it will deliver a few more MPG's than the 455 would. It will be driven on a weekly basis around town and will likely always be an asphalt queen.
The pros of sticking with the current 455 is when it's rebuilt I know it will have no other problems, It's already setup to run the Delco 24V generator and I already made a mount for the old 2 cylinder air compressor for the brakes. The cons, is it will get around 7 or 8mpg on a good day.
From those who I have talked with the 6.2 will deliver around 10mpg in this vehicle, and I plan to add super singles later. With the 6.2 I will of course have to make whole new mounts for everything. Motor mount brackets, compressor and generator. The truck already has a Th400 but it's Olds bellhousing patterned and i'll have to pickup an adapter for it. Other than that, I could probably have it dropped in and ready to rock in under a couple weeks if I don't bake to death in the heat.
So I have a decision to make, luckily I am still saving my pennies so I have a lot of time to think about the swap. They are both great engines, and the 455 has boat loads more power. But the 6.2 will be much cheaper to feed and I would love to get as much drive ability out of the truck as I can.