The rerelease uses Hotshot 2 chassis (so there's the hatch) and also the HS2 front uprights. The original Hotshot uprights are also included on the damper sprue, which they include a spare set so you can replace them when they inevitably break.
Modern side by side packs should fit, after all the hump pack it was designed for was a side by side pack inside a moulded plastic box.
There are a lot of differences between the rerelease and the original. There is the obvious different propshaft and driveshafts, and different shock metal parts, but there are a lot of subtle differences.
Rear upper arms are now reinforced, so less chance of those breaking.
New kingpins with hex drive head instead of screw slot. By not having a sharp edge to grind away at the ball cup it should keep the slop down to the standard built in slop.
E clips to hold the diff cups in place instead of those little C clips, which once you got them on were virtually impossible to remove again.
Wing mount has an extra vertical strut under it, so it is properly supported now.