The original 11-stud head could have been removed and a 9-stud fitted, but it is easy to drill a 9-stud head for 11 studs. I've done it several times for various Cooper 'S's.
I don't think you'll find an Inno with a Cooper 'S' block, but it is not important. In fact I've never seen a 1300 Inno Mini-Cooper which was not an Export, so I don't know anything about them.
Don't worry too much about the front seats. Fitting bucket seats was a 'period modification' and should not alter the value too much.
Make sure the door bins are in good condition. A lot have broken bins where people have pulled on them to close the doors. New ones are hard to find.