Installing the floor should not make the decision for you - you can still put in the step as long as the rails are there - can be bent back to shape - otherwise probably will not work if you have to put new rails in after the floor. Camping world has a retractable step that looks like it would be bolted on - to my thinking a seperate step is probably best because of the amount of weight it puts on the old frame.
It was Uwe who was bucking rivets with his wife, it is me who is going to be bucking rivets with his wife. Just ordered all the stuff - air hammer, bucking bar, rivets etc etc. Looking forward to learning a new skill (that is I hope I learn it!)
Good luck with your floor this weekend - I'll be thinking of you and sending good vibes. Just make sure you have a dictionary handy so you can put all the new words you learn in it
All in all its not a bad project - just have to man handle the front and rear panels a bit.