I'm not sure what the hydraulic relief pressure is on a 610. The more pressure and/ or flow the more hp you can put to the cutter.
I have a 5' one that was setup to run 540 rpm on my 13 gpm 2500 psi 753, it worked pretty good. When I got my 553 8.5 gpm at 2000psi, it tried it and was somewhat surprized it still worked as good as it did, even at the reduced speed the smaller pump would turn it.
Later I got a 773 with 16.9 gpm and 3000 psi, I never run it full throttle as I did not want to overspeed the cutter, it worked about the same. Then someone rented the cutter, got dirt in the couplers and seized the motor. So I resized the cutter motor to turn 540 at 17 gpm and thought lookout now I have power, but it still find plenty of things that stop or slow it down, and there is a limit to how fast I can mow with it. Especially in thick heavy grass, which seems to take more hp then brush to mow. More is always better and faster, but not as much as one thinks,
I'm sure you can handle a mower in the 4' to 5' range, you not going to be hi production, but if your somewhat patient it will work. See how much your pressure should be and then see if i can be rasied any further safely. then calculate the hydrulic hp, that will give you a idea of how much of your engine you can transfer to the cutter. I believe I now have @ 27 hp with 17 gpm and 3000 psi
The folks at www.surpluscenter.com
can help with the hydraulics