Newbie here. I'm currently refurbing a GT Arrette hybrid from the mid-90's. It has Shimano Altus shifters -- left is 3 speed, right is 7. Both are broken. Each has two thumb levers to operate it. To replace these, should I confine myself to Altus shifters, or will any Shimano do? The shifters mount to the brake levers, so that's what I'm particularly concerned about -- this may not be a standard mount (or it might be -- what do I know?)
Many thanks for your kind attention, and please forgive the newbieness.