the after market T-stat that was in the engine would barely open at 195 F

can I use an FC thermostat ? All the upper tier thermostats just list use in FC

Autozone and the like offer el cheapo t-stats, the kind designed to last for 2 years, because it is beyond most people that they keep a car more than 2 years.

Are Rockauto's motorad thermostats good enough ? which temperature should I get?

 

Not sure about the details you ask but I can tell you from reading here on the forum that the RX7 FB thermostat has a little flapper release hole that allows coolant to flow slightly even when the wax pellet hasn't opened the thermostat. So make sure that whatever you eventually get also includes that feature.


Edit: and reading a bit more it looks like it's for bleeding air and needs to be installed upright
https://www.reddit.com/r/MechanicAdvice/comments/14g8tr3/installed_new_thermostat_with_hole_upside_down/?solution=5ee5b7412ad470a85ee5b7412ad470a8&js_chal lenge=1&token=7afd7253fec22262ff1c52b1703fe9ec5d7a 933593ec5e4f8a7fdd6fe6800b24&jsc_orig_r=

Also this, but it's FC
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/how-changing-thermostat-rad-cap-683353/