^Yep same as mine, just dimples. Just gently pry it. I take mine off after a few regular cleanings to get the stuff that starts building up in that area.
As far as the mount, that is some creative ingenuity!
I still haven’t seen anyone just weld a rail to a magwell. It’s a replaceable part assuming you can get your front sight off (I hear some are welded). I have an extra magwell just never got around to buying a rail to weld on. Note My 3D printed design would require you to remove the magwell/front sight also if it was made in metal that was too thick to bend when you slip it over the tube.
Are you still selling these quad rail setups for the MK2 Sten?The quad rail(which my newer ones, were more slim lined close to the dimensions of the tube diameter) screws into the Barrel Bushing and is held in and retained in by the Barrel sleeve Latch. Like in the same way the current set up Rachets down and locks. There’s really no need to remove the rail unless your looking to replace the barrel. My advice to my customers in the past was to scrib a small line between the tube and rail this way if you remove it then you can realign it and still be able to hold zero! I’ve made and sold a dozen or so of these and have had great feedback. It’s very similar in the way you would install a handguard on a regular AR upper. Unfortunately all the aftermarket Sten parts I was making ive stopped due to my current job and family. (No time)