Before you get going with this project you should remove the head and check it for cracks. These are prone to cracking when overheated.
The heads are no longer available from Kubota but can still be found at aftermarket places. Kumar Brothers is one I recall seeing.
The head gasket from Kubota is normally recommended by the more knowledgeable people on this forum.
There is a member
@007kubotaguy that has a salvage yard for tractors and some parts for these older models. If you decide to scrap it he may want to buy it?
Try to get a radiator overheat whistle if it is missing. That is probably the only temperature indicator on the tractor unless something has been added.
Good luck and enjoy it. They are great little machines.
Get to five posts and show us some pictures of your machine.