Hmmm. Your engine does not have the heads with removable water covers, so trying to tap into the cooling system seems unlikely.
True, you could tap into the exhaust cover, but the engine runs relatively cool there, so a gage reading there wouldn’t mean much. The other problem is there is not temperature sender lead in your engine harness, so you would have to run a separate lead up to the dash, kind of messy. You could tap into the exhaust cooling chamber for a water pressure gage though, but you would still have to run the separate water hose from the engine up to the gage. I’m trying to remember if this engine has a hot light, but I don’t think it does, because there is no sender provision in the head for this.
So, you are left with the option of the surface mount temperature gage sender, or the water pressure gage.