Santa Barbara has the post-48 FN cut, through the left side of the receiver collar whereas an exmiltary action will have the full C-ring collar. Do not get too wrapped up with the extra cut in the receiver issue! I used to do the firearm safety lecture and test with a Santa Barbara action that had been chambered for .25-06 and blew up after the second .308 Winchester cartridge was fired through it. Shooter got a well-deserved surprise but his eyesight was not affected AND the receiver ring gave way in exactly the same place that you would expect from the best Mauser 98 action you could buy.
P.S. I have seen a (cast) stainless steel Tikka action (pre-T3), also chambered for .25-06, that shattered into many pieces with a single round of .308 Winchester being fired in it.
P.P.S. Absence of thumb cut is not a reliable indicator of origin. Military receivers sometimes have their thumb cuts welded up during the sporterising process.
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