Working in the auto industry affords some opportunity to check into the details a little deeper. Although you are correct about your point ("where does it require a certain casting?") I can tell you that only the 771 casting was ever imported into the US. There is no equivalent alternative. Many assume the non-federalized head with the same valve size fits the SCCA's expectation of legal but the lack of the passages for the air pump mean it is not a suitable replacement part under the rules (similar but definately not equivalent). I'll gladly wager my paycheck that a non-federal head will NOT pass teardown at the ARRC (I'll never wager against regional teardowns because I've seen all kinds of stuff squeek thru). With Fiestas you have to be very careful - XR2's were sold in Canada (not legal for SCCA racing) and with the multitude of FF and the like there are many non-legal heads around. When discussing this issue with friends at SCCA HQ (note! former autocrosser makes big time - actually some are real racers) the standard reeply is they never guarentee that you can race your car even if it's classified. So if replacement heads are unavailable then submit a request to have an alternate head approved (BAT has tried over and over). If there's no alternate head specifically allowed and you can't find a uncracked head, in SCCA's words "Tough". This is exactly whu I've horded a number of them.