James,
If you are currently towing and you are using the 7 wire RV plug and cord, you just need to add a brake controller to the coach. Most coaches already have the necessary wires ran from the LF electrical to the receiver, but since your coach was built on a Spartan chassis by SMC just after they bought Beaver, I am not certain the wires are there, but I believe that there is better than a 95% chance that the wires are there. Just locate two unused wires by the receiver area, and use a wire toner to trace them to the LF electrical bay. Then add the brake controller, connect it to these wires and connect them to the 7 wire RV plug on the coach.
Since your coach has a 5,000 pound rated hitch, if you are going to tow anything much heavier, I would either check the weld integrity often or consider have the receiver reinforced.
When it comes to the engine and transmission, the 8.3 Cummins with the side radiator that is in your coach should have no problem especially if you are careful to not lug it down on hills.
If you have any other questions, just call me, and we can discuss your issues. (713-254-4156 I am in Arizona (MST) at the present time)
Gerald