Dan
think you have already got in your head what was wrong. I dont sail a formula but things now days are much the same for all boards. Would suggest mast track in the middle, not like the old days as the tracks are smaller. With regards sail and fin combo, mismatch, a big fin need a lot of power against it, I would say a 6mt is way to small, 9mt would be better but then again in 25kts of wind!!!

Also the sail is old and will not work well with the board, now the sail have more sideways pull not front. Nose up and tail wagging, not enough mast foot pressure, basically you was shi*ing yourself and not sitting down on the sail, also part of the reason for luffing, but that can also be due to trying to get back to soon.
Keep at it, its better now that 15 years ago.
