Joel, embarassed to say your article is new to me, I want it !! You apparently have my Gun Digest article but I also wrote two for Precision Shooting, will swap xeroxes for a copy of yours.
1878, the stocks for the .22s were also available on the .30s, but had two stock crossbolts. The fingergroove stock was used on service .22 trainers, the bulker Sporter style on .22s sold to NRA members. Fingergroove stocks could be special ordered on .30s, but are rare and such rifles go for big money if they are original. I have never compared receivers but think they are the same. At least Numrich sold a conversion unit which would fit 03s or 03A3s. There was a .22 barrel liner and you got an M2 bolt which went right into the 03 receiver. These conversion units show up from time to time on the internet and at gun shows. I had one for a while, complete with a stamped 03A3 guard which took a .22 magazine. It fitted into my 03A3 but I never tried it out and it was sufficiently ugly that eventually I sold it.