We just removed an old clawfoot tub with an end drain. Our idea is to replace with a larger tub with a center drain but utilize the original floor point. Our plumber told us that Oregon code requires the tub drain to be directly over the floor drain. I have spent the last hour combing through the Oregon residential plumbing specialty codes and can't find any reference to this requirement.
The tub we are considering has the center drain exit 4.5" above floor level and the run to the original floor driain is about 33". I saw a previous post that suggested a drain slope of 1/4" per 12". With this guideline, it seems like our set-up would meet with no issues.