Willeboy
I don't guess anybody ever answered your Question.
There are three different action lengths in the series that traces it's roots back to the 721-722.
There is the standard long action, the standard short action, (which includes the 40x), and the (for lack of a better term), the super short, which includes the old 600-660 series, the XP-100, the model 7, and the XR-100. The best way to quickly identify a super shorty is the single scope mounting screw in the rear. The long and standard short have duel screws front and back.
In fact, they all share the same "three rings of steel" barrel tenon. Within manufacturing tolerances, you can just about interchange any of the barrels.
A few years ago, I went to Wall Mart and bought one of those cheap "tupperware" stocked Remingtons in 308 to rob the action off of. A friend of my sons had a old Remington ADL in 243 that had water get in the barrel and rust it. We took that brand new 308 barrel, screwed it onto the 30+ year old 700, and it worked fine...........jackie