The only thing I'm going to change is to lower the 3pt attaching points. I can lower them 8" and get closer to the height of my trailer. This will make things easier.
Raise your carryall floor instead of lowering the hitch points. You might have problems detaching the carryall unless you can always have blocks to set it on.
Build a spacer pallet, or just stack and fasten several regular ones together to try it out.
Bruce