Thank you for the photos!
I was able to confirm with my contact at Lippert that you have a 1621 model pin box so the correct Reese Goose Box Adapter Pin Box for your trailer is part # RP85FR rated at 20K. view full answer...
The only multi-fit hitch available that can fit your frame width is the Curt # 13703 that you mentioned which has a frame width range of 22 to 72 inches measure from outside to outside. The capacities of this hitch is 3,500 lb trailer weight and 350 lbs tongue weight. view full answer...