What frame, how wide is the axle? How old is it? Does it have old style slot dropouts? Pics?
I built my SA drum hubs and Rohloff14 wheels myself. Used Dyad rims, locking nipples and 2.3/ 2.0 spokes where I could. 100% solid, set and forget.
Make damn sure you don't get boat anchor roller brakes. Nexus 7i supposedly has a lot of drag anyway.
Likely cheaper to just buy a whole used bike from someone who decided it's too slow. LOL.