The newer tires are the same size and load rating as the ones you want to replace, I don't see any reason you couldn't swap them out. You should be able to get this info off the sidewalls of the tires. (If there's something I'm missing here that makes it ill-advised, I'm sure we'll find out!)
It's unclear whether you were intending to remount the tires on the original wheels. That would be preferable assuming the wheels themselves are OK...again, if the wheels are the same on both rigs (same size, same # of lug bolts, etc), you could switch both the wheels and tires.
Also check the date of the tires' manufacture...that's the code found after "DOT" on the tire...the code is the week and year of manufacture. So "DOT 0506" would be the 5th week of 2006. If they are over 5 or 6 years old they should be replaced anyway.
The jack points should be marked on the underside of the belly pan and align with the frame (so that you are in effect supporting the AS on the frame)... There is supposed to be an aluminum plate showing the jack points, but sometimes they are not there. I'm not sure on longer rigs, but our 19' Bambi's jack points are about 1/2 the distance between the axel and the rear bumper.
Some prefer to jack at the axel brackets (NOT
the axels themselves)...but I will follow what Airstream says and use the jack points (if I ever have to...ugh!)...If this does not give you the info you need...check out any numher of discussions on the topic...in this subforum: http://www.airforums.com/forums/f457/