Bob Kett's race Sprint has 2 exhaust boxes under the car. Front one in approx normal position. Rear one forward of axle. Then a pipe under the axle and exiting under the boot. It looks much better than the back box under the boot.
Then a pipe under the axle and exiting under the boot
That's quite similar to mine, except I have a pipe over the axle - partly due to the terrain around where I live
Did have to buy an appropriate mount to support the cross-axle pipe though, to stop it bouncing and overloading the mount in front of the axle. I have just a single large diameter silencer in the middle of the system.
Works quite well but I still wonder about exhaust gases coming into the cabin when stationary..........
I'm guessing there's enough clearance to permit the axle to drop, or if not, because it's racing it's not required - as they're on smoother surfaces.
Jacking, well, I don't know about the others but I alway use the diff as the jacking point....you're pushing the axle into the car so again I suspect it's a non-problem, or again, if they do jack it on a side there is enough clearance to let the axle move about or drop.