Here is the propane heater, legal in Canada and made to provide compact heat in small places.
https://www.amazon.ca/Mr-Heater-F23...53350&sr=8-1&keywords=Mr.+Heater+Buddy+Heater
You have got a lot of good advice here today.
Thinking back many years having done what you are wanting to do on a Nuffield 465 iron monster, build cab, got heater from the rear of an old luxury Mercedes and proceeded to imagine how warm my cab would be after blowing snow from an open station tractor for years.
I could get no hot water going to the heater core.
One conclusion I reached was that the core needed to be below the height of the top of the rad or it just became air locked. In the years since I became an expert in hydronic heating system designs. In those systems you could circulate water up many stories from a boiler in the basement. The critical element was "fill pressure." Think of a garden hose and you are climbing a very tall telecommunications tower. at some point water would no longer come out the end of the hose. Gravity has overcome the pressure in the hose. In the hydronic heating system, the system is filled and held at a predetermined pressure by means of a pressure regulating valve from the domestic water supply. In this way, even when off the system remains full of fluid. With your tractor, when it is cold there is no pressure to hold the water in an elevated heater core. This is why you need to have the core lower than the top of the rad.
On my newest tractor, an M7040, the heater is below the seat and then ducted to higher up places.
Lastly, and certainly not applicable on your Kubota, was the thermostat was a unique design in that as it opened flow to the rad it shut off flow to a small recir bypass line. The solution was a piece of broom handle forced into the bypass from inside the thermostat housing.
I suggest you do your install in steps. Use long lengths of rubber heater hose and connect into your system as suggested by others. Run the hose temporarily into your cab and find how high you can have the heater and still get heat from the engine. Run the electrical in a temp fashion first.
The goal to find out if you have enough engine heat available right from the start. If you don't then the heater is still in a condition that you could return it to Princess Auto.
I used rubber hose for years without a problem but do agree the concern expressed by others is very good advice.
I am suggesting another way to have protection from a rubber hose leak or rupture and that is from using ENT flexible plastic electrical conduit.
Home depot sells some smaller sizes, electrical wholesale places would have larger sizes. Slide it over your hoses, both to protect them, and contain any sudden leak.
Look forward to reading an update.
Dave