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Bill,  I'm curious as to what reason you were given as to why the modified ACA-1362 is "no longer legal".  I've found no documentation that suggests that any Standard Airworthiness Certificate issued without an expiration date is invalid as long as the aircraft is maintained as required by FAR 43.  I have heard a story locally of a FSDO inspector that attempted to confiscate an older airworthiness certificate, claiming that all aircraft had to have an Airworthiness Certificate issued by the Federal Aviation Administration and that any issued by any previous agency were invalid.  I have seen one aircraft that was parked at a fly-in with an airworthiness certificate that included an expiration date and certainly was invalid.

My Culver has an Airworthiness Certificate issued in the 1970s, but if I had an ACA-1362 that was signed, had the correct wording typed in, and had no expiration date (crossed out or otherwise), I'd want to see some FAA documentation (FAR, AC, etc.) explaining why it was invalid before I surrendered or exchanged it.  I would not exchange or surrender it simply on the word of an inspector.  I may have an ACA-1362 in my other airplane.  I'm going to look today.