It is the lower compression style. I can see two partial valve reliefs and the wider flat top. I guess the brand really does not matter at this point, but it has been a good exercise so far. I can understand about the numbers on the bottom being a batch number or maybe raw casting number to ID the item prior to machining. I would have thought that a 12.5 piston vs a 10.25 might have used a different casting rather than just machine off a section off the top. That would mean a real thick section on the 12.5 version unless also machined from the bottom??? Anyway, I'm sure I will still drive it as before. That motor makes such good music at 6000 rpms...