the questions above have been answered in other threads, multiple times http://www.ar15.com/forums/t_3_126/649481_AA_XLP_and_compatible_and_incompatible_handguards.html
and emails.
but for the sake of everyone here.
XLP works with the rev rail with no modification.
for troy rails the bottom of the rail needs to be modified to allow the set screws to be tightened through the rail. because the rail needs to be rotated, the install is accomplished by installing and gaping the gas block, marking your spot on the barrel, removing the block, installing the rail, and then installing your block.
for the Midwest SSK, Midwest recommends cutting back the spring. a Midwest barrel nut is a reversed, slightly elongated standard barrel nut. the bushing does not need to rest against the teeth of the SSK nut, it needs to rest against the outward facing flat edge. the barrel nut can simply be cut back in the one spot where the bushing rests. you do not need to cut it back all the way to the teeth.
XLP is .999 +/- tall from center bore
XLP is .565 +/- to the bottom from center bore
XLP is .97 +/- wide at its widest
as always our system is designed to work with a standard barrel nut, or barrel nut of similar length. the bushing rests against the barrel nut about .85 from the receiver. if if a proprietary barrel nut is shorter than this, a shim or longer spring needs to be used so that the bushing does not slam into the barrel nut. if the barrel nut is longer than this, the barrel nut need to be cut back in the area that the bushing rests against so that the bushing rests around .85 so that the drive rod has a complete stroke.