Just got the new 385 running after massaging oil pan with BFH, no more knocking. I put in a 180* high flow thermostat that doesn't look like the stock one with that washer on the bottom and after cruising around the temp started at 160 on the gauge and kept creeping higher after about 15 miles of 50 to 60 mph driving to a little past the center line. Do you think thats normal ? Should I go back to stock 180* thermostat? It was about 95* day here when I went out. Do these cars like the stock thermostat because of the reverse flow heads rather than the MR. Gasket High Flow? I am also running NPG+ coolant.

 

The thermostat is LT1 specific. Sounds like the one you have is an older style that would allow the bypass to be open constantly and cause it to overheat.

Either put the stock t-stat in, or plug the hole in the waterpump below the thermostat with a freeze plug.