I have the old #26 broom. I had it for my 4400 and it also fits the 3720 just fine. If you have the mid PTO, then you need to get the front (long) PTO shaft , the front quick attach hitch (with hydraulic lift and angle and the PTO carrier bearing) and then the broom itself. There was one in the classifieds here for around $1800 I think. I got mine used locally from a raceway. I paid $2200 for it complete.
If buying new, you need
1) the broom (60" broom)
2) BM19804 Mounting Frame with Drive Shaft and Hydraulic Angling
3) LVB25306 Front Quick-Hitch and Hydraulic Lift
Cost about $4600.
I had an interference problem with the mid mower lift bracket on the 4400. I had to mill about 1/2" off of the brackets. But the 3720 cleared it just fine with no mods. Deere must have found the problem and corrected it. Hopefully your 4310 has the corrected lift brackets (if you have the mower). If you already have a snow blower, then you already have the long PTO shaft and the front quick attach hitch. You would just need the broom.
Chris