I've been down this path many times in the last several years. Rear spacing on most Sturmey-Archer hubs is 115mm with a 5 3/4" axle, I believe, but you can swap in a 6 1/4" axle, throw a couple of spacers under the locknuts on each side, and you have a 120mm-spaced hub. Or you can cold set your rear triangle to 115mm. For shifters on a drop bar, there's a bar-end S-A shifter that SomaFab sells, and I have it on my '72 Super Course w/ a rear AM hub. It works great. Also, 36-hole SA AW hubs come up often on eBay, much more frequently than 40-hole rims.

Here are some of my conversions:

This one started me on the path: an early 70s Competition in Gran Sport colors:


When I sold this one, I converted more into Clubman style:


I fitted my '71 Raleigh International with a Nexus 8-speed IGH for a while, but wasn't crazy about that setup, and it's now a derailleur bike:


This Trek 412 was outfitted with a Nexus 7-speed hub and was my commuter for awhile, but I came to learn that I wasn't crazy about Shimano Nexus hubs!


I've found early 70s Super Course frames to be particularly good candidates. Here's one with a repaint:


And a '71, which is now in the hands of a list member and largely back to original spec:


And my current '72:


Though now it has the S-A bar-end shifter:

My latest creation is a Grand Sports w/ an AW hub and Cyclo 3-speed block:


And then there's the real thing:


Neal