How to Identify block and heads????

After having the wagon for around 8 months now...I FINALLY decided to go out and give the old 273 a valve adjustment.
I get out there, take off the drivers side valve cover....and I find a set of heads that are non-adjustable........So obviously the heads have been replaced at the very least. So now I'm trying to identify the rest of the motor...Can anybody let me know where the casting numbers should be on the heads and the block. I thought it was the original 1965 273 but?????