Chevrolet: car running hot, 1976 chevy nova, chevy nova

Question
I have a 1976 chevy nova that is running hot.  I have replaced the water pump, thermostat, heater core and temperature gauges.  The car came with a straight six and I replaced it with a 350 small block.  The only thing I can think of is the radiator which is made fro the smaller engine.  Could the radiator be too small and would it make the car run hot?  

Answer
Hea ;
    how is the fan ? is it far from the rad. do you have a fan schrowd , the fan should be close to the rad. I would try a flex fan. and put in a 160 degr. therm. or take it out for the summer.It is possible the rad. is not big enough.if the rad. is a small one yes it will run hot.
did you try to run it without a thermastadt in it ?? .
and how is the rad. cap ?