Wow, that mag box and follower are amazing!

On the rifle you are talking about, Bill recut the threads after removing enough material to remove the thread interruption that is present on the Model 70's. He did it to correct a grotesquely crooked LH CM receiver. Though I know he also does it with the WSM's as well. Apparently these lefty actions are pretty bad in some cases. The funny thing is I've owned three of the much rarer stainless steel LH actions and they are apparently really straight. But they were only first year production.

Dewey
I have made quite a few 4 & 5 round magnum magazine assemblies for the genuine Pre-64 Action. Some have been 300-375 H&H others 7mm Rem,300 Win,300 Wtby,458 Lott. Quite few for the 98 and a couple for Dakota's and one Left Hand Rem 700 458 Lott.