Paul,
Welcome to the group.
Regarding the mowing deck. I have a 6018. Your tractor does not have a mechanical PTO (pulley). Any deck you add will have a hydraulic motor.
There are three options for adding a mower.
Option 1
There was a 48" belly mowing deck made for the 6018/6020 loaders. Features:
1) Expensive -$800+
2) Rare - I have only seen a couple pop up for sale in the last couple years
3) OEM motors are becoming obsolete and parts NLA. A replacement motor kit will run over $750.
4) I don't know what other parts you need (deck hangers, lift cylinders, hoses, etc.) but you are looking at a sizable investment.
Option 2
HRM48H 48" tow behind (3 point hitch)
1) Nice (I have one) Come up for sale more often than belly mower
2) Price $500+
3) Awkward to use and more suitable for large open areas.
Option 3
For what it will cost to add the mower to the loader, you can have a whole tractor. Look around and find a good Case/Ingersoll 2xx/3xxx or 4xx/4xxx tractor for mowing duty. This solution really multiplies your options (mowing, blade for dirt or snow, snocaster, etc.)
Plus, the transmissions in these tractors almost never cause problems, unlike some other manufacturer's machines.
Just sayin…