Since no one has responded I will give you my suggestions.
Although not likely the case with your current engine, newer engines incorporate thermostats which not only control the flow to the radiator but also the flow through the cooling system bypass. Put any thermostat which will fit may totally defeat the design of the cooling system.
In your case I suggest you do your searching for either your Kubota B7510 or the specific engine.
Kubota D1005-E2-D16
.
eBay and Amazon.com are two possible sources although one thermostat for a B7510 on eBay is more $ than a genuine Kubota one from Messicks.
This is a 71C or 160F
Amazon
Dave