Assigned weights are shown in the link below and probably mirrored in your manual.
If you want to know the front axel you could weigh it which will give you the true weight when loaded.
A Compnine report will give you an RPO code breakdown for your coach including the front axel RPO code and factory weight.
If you are looking at the Henderson stuff, I would give them a call. I haven't installed the springs yet, but they come with a good rep and am sure they can advise on the correct application for a 35ft Chevy P30; they will have seen tons of that kind of thing.