[Bobcat]

Undy ... the only time I`ve seen the fluctuations you talk about was when I first filled my system and didn`t have all the air out ... but you`ve eliminated that as an issue .
For comparison , I`m running a 482 built by Robert Ponds , and other than carbs , it seems close to yours . The big difference I see is that Robert blocked the water pump bypass and plugged the inlet on the manifold . I called and questioned that ... and he finally told me in so many words to just run it . I also am using the March pulleys he recommended , which is a slight under drive on the water pump . Again , questioned him and he said run it , which I did .
Our summer is over , but our temps were in the upper 90 and sometimes 100 degrees . I saw 190 in town which dropped to 180 once I got moving , but no spikes . I got my thermostat already drilled from Gessford Machine .
I would be interested in what you find .... and I bet it will be one of those "why didn`t I see this before " moments .
Good luck .