You need a serial or job number to pin it down. I stamped most of the heads ive done and even the specs on occasion for those who tend to lose paperwork.
Peak# int/exh port v, etc on the outside corner pads.
The CTA 25 and CTA 26 is on the end with 1 bolt hole and in the flat pad under the center exhaust ports. I can't find any other stampings, but I am pretty sure it was manually done. Each port is also number stamped. With all that work along with the Bronze guides, 2 inch installed valve spring height with the spacers in place, extended length valves, 2 pipe plugs screwed into the intake side of the head on the end bolts, those bolt holes re drilled, a steel insert (cut off bolt maybe) in the center holes with those also being re-located, and then machined flat so the large port W5 M1 intake would work. . There was a lot of timely work done to these heads for sure.
