Which heater control valve?

The 67 to 72 water valve has no spring in its vacuum servo so it's really neither N/O or N/C.Thus it's dual direction vacuum supply.
Lack of vacuum and presence of water pressure would result in N/O condition.
The last NOS replacement I saw was 135.00
The simple solution is to use an alternative valve that is spring loaded to N/O position and use a single and correct vacuum supply line to close it. You'll have one extra vacuum line to dead end and tuck away. Or Tee it into the resivoir line might work too.
I've got 2 used water valves and both leak water. They have been stripped down and bead blasted. My plan is to replace the water seals inside.
Soldering the valve back together without destroying the seal wont be easy. I'll probably hire a master plumber with experience in such things.
Hope this helps and good luck. Let us know what works for you.