As I'm sure a lot of you are suffering from the same problem (head shakes making any ride at over 75mph a white-knuckle experience...) I thought I would share an easy fix.
Figuring out how to get it done actually took longer then the work itself. All parts were bought from ebay, with a grand total of around $100.
Here's what you need:
1. A fork ring mount. Get a 57mm if you can find one (some of the chopper/Harley catalogs carry them), or a 54mm, easily available on ebay. Of course you will need to grind it up and clear some material so it can fit the Enfield - it took me about an hr.
2. A universal fit steering damper. I got a 270mm unit to play it safe travel-wise and to match the over-all width of the fork, but you can get by with a shorter unit.
How to:
You will need to disassemble the steering lock, and cut off it's locking tab (the one that is located on the fork). That is the only permanent modification to the bike.
The steering lock frame mount bracket is ideal both in size and location for mounting the damper.
You would also need a spacer - about an inch should do it and you can get then at OSH. (please note- the spacer in the pic attached was actually fabricated, but a generic store bought one will do just fine).
The last bit - a wide steel washer, again, purchased at OSH.
The washer will slide into the triangle shaped bracket that the steering lock used to be mounted to, and needs to be cut down to a squarish shape in order to fit. You then slide the nut that secures the damper's mounting bolt to the frame on top of the washer (tight fit, but obviously doable), and your damper should now be properly secured to the bike's frame.
Other then that, the install is pretty straight forward, took about an hr, and the results are staggering...I run mine 3 clicks down from the stiffest setting (my damper has 7 levels of adjustment), and even on Cali bay area horribly-grooved freeways, the bike is as stable doing 90mph as it is doing 40. Steering stability during long, sweeping turns has also improved, with no real changes to the bike's original light handling.