My 2002 Classic had Henschen axles. I replaced the axles with Dexters and had to modify the shock mounts. You didn't mention that you were changing the axles, so there should be no need to modify the mounts. The axle will just be a little lower.
The lift kit is a different question. If you have Dexter axles you should be fine. If not you may have to modify some combination of the trailer, lift kit, or axles. In my case we slotted one hole on the axle bracket when I changed axles. We then had to slot one hole on the lift kit to get it to mate up with the trailer when I added it later.
ďYou cannot reason someone out of a position they have not been reasoned into"
Al, K5TAN and Missy, N4RGO WBCCI 1322
2002 Classic 30 Slideout -S/OS #004
2013 Dodge 2500 Laramie 4x4 Megacab Cummins