OK folks, talked to Mor/ryde today and had a very nice conversation with the gentleman that assisted me. I now know that I have 8K rated Mor/ryde axles that were installed at Mor/ryde (not Las Cruces) on our MR. Apparently, standard axles were put under it temporarily to get it back to Elkhart for repairs.
I'm extremely excited to learn it does have the heavier axles. He also told me there are three levels of rubber springs in the Mor/ryde IS system, an 11, 30, and 35 with 35 being the heaviest. He could not tell me which were currently on the fiver but told me how to determine which I have. It appears we have the middle range spring which from what I learned should be more than adequate for our needs.
With that now known about the under carriage on our MR, I plan to take the suggestions on this forum and up size our rims to the 17.5 with GY G114 H tires and remain a two axle configuration. Our current 16" GY tires are only rated for 3750 lbs @ 110 lbs.
The jury is still out at this time on reinforcing the frame with 2x2 tubular steel.