the 3/4 and 1 ton models are on the same skeleton. The 1 ton will have an extra leaf in the spring pack. Another thing that may be hindering your tow capacity is the 355 gearing. If you contact Ford they may tell you what effect changing to 373 or even 410 gears may make and what changes you can safely make to the suspension. They may also go cya and tell you you can't do anything. It could be worth a phone call or email. If you decide to go with a bumper pull you can easily manage 10,000# plus with that truck.
Good luck!