UPDATE,
worked on it today

I bought and Installed a mechanical gauge today. So far , so good.
I also put an overflow bottle on it so it doesnt mark its spot anymore As the rad cap is a newer model designed for a return system .

Got it all warmed up sitting at high idle ,,,,, and the stock dash gauge needle pointing straight up the mech gauge is showing right at 170ish . Im gonna run it a while and see where it operates regularly . Im really starting to think im chasing a bad gauge or sending unit.