if something is wrong with the drive side 75 then you should be able to use the grand mighty without trouble (i think). it certainly won't f up your bottom bracket, you just have to worry about your Q factor being off (the distance the crank puts your pedal from the centerline). if nothing is wrong with your 75 crankset and you just want to have a "grand mighty crank" on your bike, then just ride the matching set. no one is going to **** on you for 75's