Head ID help??

I have a BBC in my 47 Chevy coupe, and i am wondering what heads are on it without pulling the intake please help. Casting number is 3993820

 

they are 1971 oval port from a 402

 

Are they any good to make power?

 

3993820 400-454 71-72 Oval Port
820 255/114cc port
2.06/1.72 valves, Closed Chamber
They came on LS3 and LS5 330/365 HP motors

Many consider them to be about the best oval port castings you can get from the factory. Up to about 6,000 RPM they flow great.