duramax centerfeed

I have an old B&C blind mag Duramax that I know I got working good a few years ago with a centerfeed 110. I trade components around a lot, ended up with the stock on a staggerfeed and now want to put it back on the centerfeed. There is clearly more space than needed in the magwell and no slot for the L-clip but I must have worked through all that before. The magazine is flopping around in the well and also sticking too far up, impeding bolt travel. The L-clip would solve some or all of the problem but since there is no recess for it in the bedding surface, it makes the tang stick up and/or prevents the front action screw from engaging.
This is proof if proof were needed that I am getting dumber by the day. Can anyone tell me what I'm forgetting?

Tape the magazine to the action with a business card between the feed lips and bolt to get the correct spacing. Put four small balls of plumber epoxy putty in each corner of the magazine well. Put some release agent on the metal magazine box. Assemble the action in the stock pressing the correctly positioned magazine box taped to the action into the epoxy putty. Wait 10 minutes for plumber's putty to start to set up. Remove stock and magazine. Trim up excess putty before it can harden completely. Now you have a snug base for your magazine at the correct height in the stock for proper feeding. The old stagger feed stocks have oversized magazine wells compared to the center feed stocks. Put a small wood screw in the grove on each side of the magazine and in will stay in place once you add the follower with spring. Problem solved.