I don't see why you couldn't. The plates come powder coated with the top side being well finished and the bottom side not so well finished so the grounds can connect to the chassis properly. You would have to sand one down and powder coat the other side.
If you didn't have any issues building the mirrored Paramount, then building a mirrored MonAmour shouldn't be too tough. Things will change a fair bit in terms of 4 pin socket wiring, as you'll have to mirror the socket as well so the filament pins still face the hum pot (you probably did this for your Paramounts as well).