I have two LHD cars, not Z's, I've considered swapping to RHD.
Only two real issues with swapping.
Steering rack
Wiring
Rack is not a problem as lhd/RHD cars exist. Simple swap.
Wiring is a problem as the loom is made to fit, so, you either need a loom from the opposite car or, you 'flip' the central part of the loom. Which I wouldn't recommend as there are an awful lot more wires in BMW loom than you think.
If you have a dead donor, you "simply" swap all the LHD bits into the live RHD car.
Rack, dash, speedo, wiring.
The Australians use chain drive systems to swap American cars to RHD and extend the wiring