The IMS 17mm fits with little to no modifications. However, the IMS 20mm can also be filed down to fit and gives a brighter hotspot due to the larger diameter and depth.
Get rid of all the legs, file down the length from the open end of the reflector and slim down the sides of the reflector until they fit. I used a fine grade file to do it by hand. Took about 2 hours to fit it, but the results are worth it. Fits the Mag 2AA head much better than the 17mm.