I have a set of W2 heads that I need help identifying from the attached pictures. The previous owner ground off all of the exterior cast numbers. The casting number is still present on the inside of the head, but I believe that same casting was used for a couple of different PNs. There's a 4 digit number stamped on the end of the heads too but I'm not sure if that is something that someone added. I'm a total newbie to W2s so any help would be appreciated. Thanks!

Also, in the parts deal I got a 340 block dated coded 6-20-67. I imagine that's pretty damn early in the run for the 68 model year. Anyone happen to know what the first production date for the 340 block was?