A good thing to do would be to read over a few of the recent posts and you will see that this question gets asked a lot and the answer is complicated. A simple answer is that all the 400 blocks are the same 67-69 and that would be a good start. Another easy thing to do is to look at a chart that shows 67-69 400 engines and heads and their codes and see which 400 engines had the HP/compression you are looking for. Then note the head code and look for that head.
Jim