I used YSS cartridge valve emulators.
Pretty easy to install, but you need to shorten the springs (cut and grind flat) and drill the pumping rods. You also need short tubular spacers, which YSS will cut for you for a small fee.
My first time write-up:
http://www.enfieldmotorcycles.com/forum/index.php/topic,15188.msg163193.html#msg163193I then switched my fork to a disc brake unit, the type with the fender bosses in the sliders. (Not the strut-mounted type.) I needed the next emulator size down for these, which was a bummer; the tubes are slightly thicker-walled.
Race-tech can sell you emulators and springs, I think, and they are the USA-made original. YSS is a clone. But race-tech has never answered a single email I've sent; since I was overseas I preferred email to phone, and YSS USA support was very, very helpful.
Mikesxs.com also sells a super-cheap emulator.