I currently run a 472 Brown cutter with a Ford 4610 SU and WorkMaster 50. Both tractors handle it just fine. The Brown specs out at 1095# with a 120 HP gearbox.
I talked to a friend of mine that sold a late model Ford 3930. The 3930 has the same engine that is in my 4610 SU. The engine is rated at 52.52 HP at the PTO. He tried running a 10' cutter with it. It required reviving the engine up to engage the cutter and the tractor ran hot after 30 minutes of cutting. The overall condition of the tractor was good. I believe that he was spinning a 10' Bush Hog brand cutter.
IMHO a 10' cutter would be putting your 55 on the edge based on cutting conditions and surrounding temperature. An 8 foot medium duty unit should be fine with proper front axle ballast.