Just for those who might someday have to tread this path: I tried opening the v3 files in FM5.1.1, and no joy. That far back, the "heroic open" doesn't even exist. I tried opening the v3 files in FM5.5.6, and the "heroic open" fails just as it does for FM7.1.
Since Scott Prentice of Leximation has very decently offered to see if FM4 will do the job, I still have hope. (Also glad I bought his BookVars plugin.)
