I've had success with the Fel-Pro copper head gasket and used no sealant.
I also removed the head twice and reused the old copper gasket with no problems.
Did you torque the head bolts in the correct sequence and a little at a time. And then the final torque at 70-80 ft lbs.
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0611.htm
