That sounds reasonable.
The barrel extensions should be tightened to 100-130 ft-lb, but may have been assembled with red loctite as well. Either way you'd need a decent barrel vice and an extension tool to remove them; I use the Brownells "reaction rod" that is sorta like the Geissele unit but only $60 and works really well. If they have red loctite on them, you'll have to heat them up a bunch to break that bond; maybe more trouble than it's worth.
IF you want to loosen the barrel extensions, you can insert a go gauge and your stripped bolt and screw the extension back on just snug against the bolt. Then use feeler gauges to measure the gap between the extension and barrel shoulder; that tells you how much deeper to run the reamer in. That's my normal AR barrel chambering practice anyway.
For this though, especially since you've done Mauser barrels and are used to taking the last little bit by hand, I'd be inclined to do it by hand and leave the barrel extensions tight. It's not much different than doing a Mauser, except that you have a lot less camming surface with an AR bolt, so just go in small steps and check frequently and watch the bolt start to cam in when you get close.
Don't use a piece of brass as the go gauge of course - you'll usually end up with a short chamber if you do. 4D Reamers has the gauges for rent if you don't already have them.
My preference is to mount the barrel vertically when reaming by hand; it seems easier to keep everything straight that way.
Last edited by Yondering; 10/17/19.
