Conversion vans tend to be a bit heavier than passenger vans, but yours isn't too bad, since the original empty van was probably around 5600-5700 pounds. That is the source of the "6400" number, 12,000 - minimum possible weight of an empty van = advertised towing capacity.
Loading the van to GVWR of 7200 (which includes tongue weight) gives "maximum towing capacity" of 12,000 - 7200 = 4800 pounds. You don't have a lot of wiggle room. Even though you would not be so close on the weight if you had an Express 2500 with, say, GVWR of 8600 to 9000 pounds, the same drive train would keep GCWR at 12,000.
Express can be an impressive tow vehicle, but only with the right combination, Express 2500/3500 for the weight carrying capacity, 6.0 V-8 or Duramax to bump GCWR up to 16,000-17,000 pounds.
Ford E-350 vans with 6.8 V-10 push the GCWR to 18,000 with the right gearing, and thus might tow as much as 9000 pounds when loaded to 8600-9000 pounds. But even that van is down to 15,000 GCWR with the V-10 and economy gearing.
I have a E-350 passenger van with V-8, 6300 empty, 9500 GVWR, 13,000 GCWR for "towing capacity" of 6700 pounds. My target weight for any towable RV would be 4500 or less, so as to retain carrying capacity for eight humans and their gear (I stripped out that 200 pound back seat). What I had in mind when I bought the van was a Casita or a hard side pop-up camper, well under 4000 pounds.
Tom Test
Itasca Spirit 29B