New motor Probblems

I have a 1977 ford thunderbird milage 49849 with a 2004. 351w not modafied that was installed in 2004. After driving the car aprox. Three years I had to replace the trans. My probblem is that I just replaced the copper core radiator with a new alummium radiator and after flushing the block and installing the coolent and toping it off with water. I let the car run at idel for about 45 min checked the temp gage and it was reading halif way hot. I turend off the car took off the rad. Cap and saw no water. Restarted the car addid water and turend it off for about 2 hours. When I returend to replace the plugs and whires starting at no.1 plug was normal ware no.2 when removed Leaked antifrezz from hole. Is this a Blown headgasket or what im at a loss