FT - half the power of your stock 250? Don't tell me that!!! What is your distributor out of? Stock, HEI? As Tony said, sounds like your timing may be retarded.
As for the temp guage, if your cooling system has an air pocket in it, you should have still seen something on the guage. Did your thermostat have a bleeder hole in the upper quadrant to let air pass through? Are you getting flow through the heater core?
