The thing I don't like about the factory set-up is the shower walls attach to the outside of the pan. Why didn't they make them overlap INSIDE the pan? Then the sealant wouldn't be so critical to keeping all the water inside the shower...
For now, that's all I'm changing on my 74. When I re-do the shower stall walls, I'll lap them inside. And if I have to replace the pan one day, it will depend on how functional I thought the original design was. I've seen some pretty cool bathroom mods on here.
Don't know how far you're tearing your trailer down, but it shouldn't be that big of a deal to change the drain location if you've got the belly pan off... but quickest and easiest will be to order the same thing and put it in.
Somebody ought to clean these windows. There is a tremendous buildup of gook all over them...