I don't know what model of ZF marine tranny those guys are using but a lot of ZFs have the same kW ratings in both ahead and astern modes which solves a LOT of problems dealing with reverse rotation engines. Basiacally, you just install a LH wheel on that side, rig the shift linkage backwards and cruise.
Edit:
ZF63A marine transmission specs
The reverse ratio is slightly different so you have to pitch that wheel a little differently than the one the is running in "ahead" mode.