I have a couple of actions that have lug setback on mostly the lower lug. I had them tested and one tests R38, one R45. The Rule book says they were heat treated to an average of R47/48. There has been a discussion numerous times about hardness/brittleness of these actions. I want the lug abutment in the action machined to remove the setback. My smith says it can easily be done. How soft is too soft on a Pre-64 action? Can it be compared in any way to the Mauser case hardening at R35-38????

I will give you a few bits of information for you to consider.

A good knife blade like a Buck, Kershaw or Western tests about Rockwell C55.
A file will be about Rockwell C64 to C67.
A piece of REX 95 tool steel is about C64. Rex 95 is used for hand ground lathe tools ... to cut other pieces of steel.

I Rockwelled a M700 Remington bolt on the locking lugs at C44.

I can imagine a little wear on the lower lug recess on a well used rifle but I cannot imagine how you would set it back unless subjected to significant abuse by a reloading overload.
My M70s ride primarily on the lower recess because the force of the cocking piece on the sear pushes the rear of the bolt upward.