ITT: you will provide links to a 3/8" barb remote thermostats
 

so I can put one on my heater line.

Thanks,
Dad

Just an inline tap will do it. I haz got one in my build thread. Reduced to a bare minimum and heater hardly functions now.

/thread

I just clicked through 11-pages and apparently we're not talking about the same thing. I want to keep it from running so cold, but want to be able to get more flo when I'm at the track. I've thought about just adding a ball valve.

Heater hoses are 5/8".

Love,
Mom

In a post on MF I described a setup using a Mocal oil 4-port t-stat. If you choose the right 2 ports (and plug the other 2), you will get what you need - flow when cold, no flow when hot. It has 5/8" NPT ports.

Ok, it's not there then probably. It is here:
https://www.miataturbo.net/forum/t35890-2/#post422761