The "J" is an inbetweener. Those came out when Savage was trying to standardize their short and long actions. 10,12,16,110,112 and 116.
Like boots mentuioned, different action screw spacing. One piece scope mounts are few and far between unless you go to a rail mount. Same with different style stocks. A short action stock can be modified by moving the front mounting screw hole (in the stock) forward about 1/4".
Bolt body length is a "one of a kind". Bolt head and handle are the same as any of the 10,12,16 or long actions.
My first Savage is a 110V that started life in .223. Been about 5 or 6 different calibers since then. From .221 Fireball to 6.8 SPC. Couple of different stock changes also.
A one piece scope with rear windage adjustment was not available (after a long search) so I had a smith that I knew build me one out of a couple of new mounts. Cut, weld, polish and it couldn't have turned out any better. Got it just the way I wanted it!