Spocalc has S-A 3-speed hubs in its database, as well as lots of rims (though I'd still measure the ERD of the rim to be sure). Traditional Raleigh Sports rear wheels are laced 4x, but if you're not a heavyweight, 3x will be fine. FWIW, I've never used washers to reinforce the flange as is recommended, and I have yet to break a spoke or flange on one of those wheels, but I haven't necessarily subjected them to lots of stress or weight (I'm 160 lbs).

Neal