5th wheel with Class III hitch on back - Excel - who else?

I notice that Excel is careful to state that it can PULL 4,000 pounds with the factory-option hitch..link. No mention of hitch weight carrying capacity, though. Not sure if one could put tongue weight there for a 4,000 pound TT, for example.

They do also offer a presumably higher-weight carrying capacity "Hydralift" receiver that's capable of carrying a touring bike. That class of bike generally weighs five or six hundred pounds...dunno if that hitch can be used for towing, too.