Mod the Geissele Mk4 to work with the Lima6 and RifleSpeed gas blocks.

You will need McMaster Carr 8492A262 and a 3/8" drill bit, just like with Lima6's version of this that works with Midwest Industries tubes.

This only cuts the groove for the RifleSpeed gas block to fit into. If you're not using a RifleSpeed or other straight tube gas block, you won't need this. You will need to do the below mods still though.

You will need to cut off the anti-rotation tabs, and if you have a newer Geissele with the steel reinforced sling swivels you will need to relieve the back of the insert on the left side of the rail.