Under the valve cover there should be a part number 2531100-M (the A990 heads are the same part number without the -M). The newer heads should have a fancy "E" cast somewhere on the head denoting EDELBROCK.

When I spoke to Tim at FHO with regards to my particular problem, he mentioned that there was a real problems with sizing on the guides from the folks who were machining the heads for MP (I think it was Dart). Ditto on the valve seats.

I would still have a look at the seats. I had a friend of mine that was working on an engine with a set of factory '65 A990 heads. The lash kept opening up on one valve. They pulled the head and found that the seat was starting to drop out. They caught it before it became a disaster.

I wish I could post pictures, but they are too big.