The shock isolated bezel is slightly larger than the stock one and has a section of foam that acts as a cushion to absorb the recoil so it doesn't damage the lamp.
You need either an XM or UM tailcap. The XM has both a regular pushbutton and the removeable pressure switch and the UM is the pressure switch only. I think the standard length is 7 inches, but other lengths can be ordered.
But, these are about $100 MSRP. Pelican makes a tape switch that sells for only $20. I don't think that these are the quality or have the durability or longevity of the SureFires, but as long as they are reliable, they are great for the range or even home defense where you aren't subjecting them to tons of abuse. It's not like a tape switch is some high tech device after all.
Is yours a 6R or a 6P with the rechargeable kit? The body of the 6R is solid, while the 6P plus kit uses an add on extension for the longer ni-cad battery. Both use the P60 lamp. If it's an older 6R and it has direction it might mention the R60 lamp or might have come with one. Those have been discontinued and the standard P60 is for both the rechargeables and lithium batteries. You can use lithium batteries with either. Remove the extension if a 6P, or get an aluminum spacer (or make your own, a chunk of aluminum or even a dowell with a strip of copper) if it's a 6R.