Like SteveM pointed out.. the pto on that unit turns backwards. If you get an implement for it.. you either need a gearbox reversor.. which are expensive to build or hard to find ( a few were available ), or you need an implement designed to work with that backward pto.
Not sure what finishing mower you have or its blade / pulley arangement.. but perhaps you can change the belting at the pullies and make it where the blades turn the correct direction.. might need a longer belt to make the swap... alternately.. perhaps you can mount the blades backwards?
I've seen a few cob-job setups for a reverse pto. Even a rotary cutter with the blades backwards. I'm not sure how they did it.. if they were straight blades it would have been pretty easy..but if they were bent blades.. I'm sure it was a finagle..
Soundguy