I have done this but don't recommend it especially for a gravel grinder.
I needed a cheap quick way to upgrade to 8spd for accompanying a customer to work, sort of like a Domestique arrangement. I put long axle in a CampI hub with a Sachs 8spd FW. It worked OK with his Ergo group but I did go through an axle or two over the years I had that setup.
Decent shipmano STX and RCS level hubs are cheap and you go either 7 or 8 spd.
__________________
“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk
Last edited by Bianchigirll; 10-06-14 at 07:15 PM.