Interesting thread.
Nice to see some people doing actual measurements instead of just "argyin".
The "fixes" are simple, but probably noteworthy. Were it me putting an A&B "Savage" barrel on a Marlin action, before installing the barrel, I'd opt for dropping a gauge (or case from my reloading dies), in the chamber, measure the protrusion, compare to depth of bolt face, and either 1) turn the excess off the breech, 2) ream the chamber deeper, or 3) leave alone if within specs. However, 1 and 2 are not available to the "regular Joe" just looking to "drop" an aftermarket "Savage" barrel on a Marlin action.
I'm not one to 'worry' about headspace too much. However, one of the great "things" about "building" one's own rifle is the ability to put into it all the precision you can. While I don't "worry" much about headspace, I AM a nazi when it comes to setting the headspace on a rifle I build. To be sloppy with headspace is to be, well... SLOPPY. To me, that seems contrary to the concept of "do it yourself".
Paul
