Rebuild ideas and thoughts

I agree with what Ron said a TBI would be better. Also add headers and get rid of the stock exhaust manifolds they are probably leaking or cracked, you will increase your HP buy roughly 80 HP. Add some air dams from the grill to the radiator to force air through radiator instead of under neath it to keep it running cooler. Add a CAI to grill instead of stock intake which is sucking in hot air. Advance timing from 4 degrees to 9 degrees to pick up some more performance. I would not worry about the long drive shaft, you have more important things to do. I would not worry about the tranny or adding 4 wheel drive you have a lot of weight on those rear wheels for traction. The 4LE80 transmission is fairly robust, just change fluid and filter and look what is in the bottom on pan before you rebuild the transmission. With 64k miles it may just need a fluid change. As far as the body you are asking for a lot of work that won't add much value for you. Weight the MH first and compare your Traveling weight to you GVWR which is probably no more than 18,000 lbs. Remember if you are living in the MH with all your tools it will be a lot heavier than just a week end camper. How long is the MH?