I have a 763 with factory cab closure and heat. I notice needing the heat to act as a defroster for the glass, the heat is to the left with 2 or 3 vents right there, nothing under the seat or on right. I have a s150 open rops I was thinking of enclosing but limited budget- may pass and invest otherwise into tires or attachments. snowblowing! nice I have been searching for one around these parts but havnt seen a used one for sale yet. the snow box gets heavy fast........What is your budget? Are you looking for an OEM solution?
There are low budget soft plastic kits available that will get you closed in. Adding heat could be a bit more work / $$.
I found with my machine, closing it in was enough, at least keeps the wind blast off of you and keeps the snow off while snowblowing. I get a bit of heat in the cab percolating up from the hydraulics.
HTH - SR