Sorry for the long delay getting back to this thread. I had a lot going on in my life. New job, new house, etc. Anyway, jumping back in head first into this build I picked up some necessary tools and parts I needed to get moving on this L4. This whole thread was about the ring/bushing/spacer object that was protruding slightly from the barrel socket. Well, after quite a bit of frustration and persuasion with some prying tools and a blacksmithing hammer. I removed the bushing from the barrel socket. This needed to be done as it was cocked and then welded at an angle due to building up weld on the top front area behind the barrel nut slot and not seeing it in the first place. Luckily, its a very simple bushing and machining a new one shouldn't be too hard. It seems to have originally been a .001" press fit into the machined area of the face of the receiver. Seeing as I have enough of the bushing left to get a measurements on it. I should be able to replicate it in a few minutes on a lathe. The difficult part now will be to machine out the counterbore that the bushing fits into. When I built up weld in the area directly above it, a piece of it was welded to the top side of the counterbore leaving some of it permanently welded in. I will either have to get creative with my mill, or very carefully remove the rest with a rotary tool. If only I could get my hands on a full set of blueprints for this thing. I've scavenged some pictures of old blueprints for Brens, but most of them are very hard to read.

Brit plumber, sorry for the delayed response to your question. The recess for the front lip of the magazine is untouched other than some weld slag that can be easily removed. I picked up a couple of (surprisingly expensive) L4 magazines that are in good shape. I should be able to use these the get me in the general ballpark of placement of the receiver pieces.
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