hey Ryosuke I have a 16" thermo on my R31 & works a treat
I might be able to get u one cheap but will have to look into it + u pay freight cost.
send me a PM if u want me to check into it (brand new by the way & not hot)
I am using a old mits colt thermo switch for the cut in/out, 85 deg (give/take) 5deg+/- 74 deg +/- 3 deg,
I had a 38mm exhust pipe made up thats 2" long placed in the top hose with the switch/nut welded into the pipe, as the clutch fans on the RB's run a heat clutch in them so there is no way to get a switch in there any other way + plastic tank on the Rad means the copper probe is not the best idea as u can bust the top rad outlet trying to over do the clamp to stop leaks
also the switch is a 1 pin switch so u will need to earth the pipe out so once the switch opens it earths out through the pipe
Hope that helps a little
Cheers Mike