RJW in NZ:
I have been watching buttons going through blanks a bit lately.
The initial run of 20 P-14 barrels is just about finished to profiled and threaded state and then we move on to SMLE and No5 barrels. No4 barrels are bit further away because of the issues of indexing and absolute headspace reference.
It is all happening on a very malnourished shoestring, but it is happening.
The biggest problem is not with the barrels but with the condition of the original bolts and receivers. Too much wear on the locking shoulders in the body and the effort of rebarreling is fairly pointless, regardless of how many No3 bolt heads you own.
However, if you have a "bitza" No5, a 7.62 x 39 rework will be a hoot. That style is where the M-10s started. Mini-30 mags work fine if you can get them. Alternately, if you have a stash of AK types, these can be used but with the reinforcing plates carefully ground off the top sides of the mag body. The controlling feature is the width of the existing mag well. I have never been keen on thinning the receiver side walls in rear locking actions. Previous notes about mag spring tension apply. Your biggest problem will be modifying the bolt head to run with the dinky rimless cartridge.