</font><font color="blue" class="small">( Thanks Dennis, I would like to purchase a 84" rear mower.
I don't know if the 855 can handle it.
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If your 3PH has the weight capacity and your lawn is groomed regularly, you should be able to operate an 84" mower. Befco recommends 20 to 50 HP (PTO) for their 84" unit. Your 855 has 20 PTO HP, so it should work. Worst case is you may have to make partial passes or go a bit slower if the grass is thick.
The Befco weighs 690#, so your 855 can handle the lift. If you don't have a loader, you'll definitely need front weights.