I do have that hose, it's 3/8 and my heater is 5/8 I was afraid it would be too small to supply the heater, Maybe if I remove?
Yup, same as mine. I ran the larger hose from the heater to just outside the cab framework. Then with a couple of barbed reducers converted to 3/8" hose for the rest of the way to those bypass fittings. There was plenty of heat supplied to my heater and the smaller 3/8" hose was much easier to run under the hood and up to those bypass fittings. I can't be sure if my heater fittings were 5/8 or 1/2 inch, but either way I think you'd have plenty of heat available to your cab. I'll see if I can find the specs to my heater for you.
David
Edit: Here you go:
Kubota B2650 Cab Fabrication | OrangeTractorTalks - Everything Kubota
Starting at post #42 describes the heater I installed. You could google more of the specs to compare it to your heater. You can't see it in the pics but the barbed reducers are just outside the cab wall and hidden behind the loader post. I think the steel barbed reducers were around $4 each, give or take.
Let me know if you want more pics or any other info, but I was more than happy with the heat output through those 3/8 inch hoses. I use my winter fronts on the tractor hood and when the temps drop well below zero, as in -20F and colder, The heater can still have me in shirt sleeves inside the cab.