Darrin, I am swamped with projects for the wife and myself but for you or Tom I can find some time to help.
First, How long is your barrel stub, I assume it has the correct thread to screw back in to the reciever , correct ?
Are you talking of using the GM 40 cal. blank that is about 1" dia. X 20" long ? I made a handi barrel with that blank and shot .401 bullets out of plastic 410 casings to be a OH legal deer gun before we got the strait wall rifle rule.
I just happen to have a 40 S&W / 10 mm profino reamer and could come up with a tool or reamer to throat it depending on what kind of bullet you intend to use. Just in case you have never heard of it Starline makes 10 mm magnum brass also.
I have a barrel chambered in it for a profino zip gun I built, hence the reamer I spoke about. Don't think it would work with 45 ACP mags though, to long OAL.
Are you wanting to put this back in the same stock from a original 93 Mauser, even though I know it will be customized by your great woodworking skills ? I could do a strait taper on the blank from the end of the stub to muzzle without spending weeks of time to do a actual profile like modern guns have or could turn it the same diameter from the front of the stub to the muzzle.
As far as head spacing the barrel I think we would have to see if the bolt face needs modified first as I do not remember if they are flat or if they are recessed or something else ?
I can tell That I am already getting to long winded thinking about this . My wife and I are going to FL like always around the end of this month for a couple weeks. I will send you my email address and home phone when I get back and we can discuss a bunch of details.
Once you actually own a true profino firearm you will learn all of the secrets that manny and red have passed down.