Change is never fun. Sometimes it is a royal pain. My last Juno switch was years ago with my father in law. It was not fun, but there was some good info in the Juno FAQ’s online at the time. If you have backups of the 150 separate files, work from the backup files instead of the one big file. Do you know what those 150 files were before they were merged? Windows often accumulates file fragments (incomplete files left in memory – especially if the power goes out during a session), some of the maintenance software puts all these parts into one big useless file.
I have successfully used the “spinwrite” software to recover data after a drive crash. It can be purchased from their web site and downloaded. I can’t say for sure I got 100% but I did get a lot. Cost was I think around 80-90 bucks, and it ran for about a day and half, and when it was done the drive was functional again.
Wish you the best,