Best way to deal in reading very old xls files

I'm coming across transferring and old app to a new one, some of the reports are generated by some very old desktop app running on old xls files, the new app is build with rails 3.x but the only problem I have is that it keeps on getting an OLE Signature error, I tried parsing the files manually via excel to xlsx and all the rails xls gems start reading them. What would be the best way to handle old xls files?

1. Are there actually gems that read very old xls files, I've already tested roo, spreadsheet, rubyXL (i can't get simple-spreadsheet to work due to version conflicts with roo-xls and spreadsheet requirements)

2. Gem that would allow me to simply re-parse the file as an xlsx file and let the latest gems read them from there on.