So I was trying to take the drain plug out,soaked it for a couple days and still wouldn't come out. So I heated with a torch and the whole think came loose. Can this be soldered or brazed back on

 

Not by me, no.

 

I'm assuming (hoping) the tank had been thoroughly flushed?!

I'd have a new pipe-thread socket put in, while the tank is inerted with CO2 or nitrogen. Brazing is likely better, and with a reinforcing pad around it.

 

Oh yeah tank has been empty for 25 years left open and I flushed it out

 

You can get pipe flanges for brazing/soldering. I have made fuel tanks using these.
Black WeldIn Scully Flange

 

Thanks Mixer man i was just looking for these and i seen this thread. What luck. I couldnt even think of their name.

 

There are also Weldolet and Flangolet adapters too, but for heavier applications.

 

It can be soldered in just like a radiator repair. I changed the filler neck in my trucks original gas tank and also changed the sockets in my blinkers. Use tinning flux to prepare the metal for soldering . In my albums there is a pic of the gas tank neck replacement.