Jake,
Here's a couple of rays of sunshine for you .. possibly...
I run a
1972 GMC 9500 road tractor. It's insured as an antique/collector vehicle with Gulfway Insurance (they're listed in out Links section. It has a commercial 5th wheel, but it also has a gooseneck 2 5/16 ball on it that I usual hook my 20-ft g/n flat trailer to so I can haul another truck to shows, etc. Even loaded with Grigg's diesel conversion truck, I'm still easily below 26k. And because Maryland issued me a title for an antique vehicle rather than a semi tractor, I can still use the Antique plates.
So, even though the DOT regs are confusing, and not evenly enforced or even interpreted from state to state, I'm told (but can not confirm yet) that as long as I'm under 26k, not using the commercial 5th wheel and have antique tags, I am fine without the CDL (should have the medical card, as anyone should, for vehicles over 10k I think). Again, this is anecdotal but it sounds good

I ran 700 miles to the ATHS National in this configuration and went through several scale houses and didn't get stopped once (doesn't mean that I won't, just saying on that one run, they took a look at me and decided I was okay).
My point is to consider a different hitch from the commercial 5th wheel to stay out of commercial vehicle territory. Maybe using a g/n hitch and trailer would do it? There are some pretty beefy g/n flat trailers on the market.
Both Mike B and Crenwelge know my truck and can comment on this as well.
To see my g/n hitch in action on the ride home from So. Bend,
Check out this short video clip (The background music in that video is a 6-71 Detroit at 2300 RPM, foot on the floorboard

)
Hope this is food for thought.
Regards,
John