The tow rating dropped with the watts linkage 4-link suspension design in '98.
There is nothing inherently worse with a watts-link design than there was with the splayed 4-link design of the cars. The roll center is lower with a watts-link but that would help, not hurt, towing. The watts-link would provide way better side-to-side stability than the splayed 4-link and that should do nothing but help towing as well.
Either Ford was concerned that big pivot stud on the 8.8 axle housing wasn’t strong enough to resist a trailer pushing the tail around or they were just being overly conservative. either way, I’m not sure I’d risk this.