Cooling issue, but this time it's to cold...

I've had the car out four or five times since I got it back from Rick, it's got plenty of heat now. Seems maybe the timing being slightly retarded and carb lean could have been the issue because the problems gone.
Maybe you're just driving it more and a bit harder with the good help and the confidence that gives. Retarded and lean normally lead to being hotter, not cooler.

Time for a new gauge IMO to be sure. Here is why FWIW; engines are designed to be used in a certain temp range:
http://www.carnut.com/ramblin/cool3.html