I have a 7 speed Shimano freehub, 13 to 24 teeth. I want to fit a 27 cog on its own or a cassette that I can use or cannibalise. If I have to use a 28 tooth then I will need a 25t as well. I understand that I can use Hyperglide instead if I grind one of the tabs that fit the splines. Has anyone anything that would possibly suit me? Or advice........