That's the same head that I have on my 270, it is used with the flat top pistons, with the slight dish in the center.

there should also be a date code cast into the head also, that will tell you when it was cast.

They were used on 54-59 248 & 270.
Here is some info on GMC heads
http://oldgmctrucks.infopop.cc/eve/forums/a/tpc/f/462107036/m/71520754563

Last edited by JeffL; 01/10/2016 10:51 PM.