There are only two Winchester sets of bases for the #2 (and #1) mounts to my knowledge. One set of bases will mount an A5 on 6" centers with the rear flat bottomed base set on the rear of the '03 fixed rear sight base, and the other set (Marine Springfield bases) will mount an A5 on 7.2" spacing with the rear curved bottom base mounted on the receiver ring. I know of no other bases for the Winchester #2 mount. One might ask why the different spacings. Based on what I have read, the 6" spacing preceded the 7.2" spacing, but it really makes little difference. Out to a bit less than 1,000 yards, the 7.2" spacing has the advantage of simplifying windage adjustments (1" impact movement at 100 yards, 2" impact movement at 200 yards, etc). But at 1000 yards, limited field of view causes sighting problems as to elevation (keeping the crosshairs on the target). At this point, the 6" spacing has the advantage due to greater vertical movement per incremental "click".
But why mount the rear base on the receiver? Simple. If you have ever D&T'ed an '03 barrel as I have, you know how thin the barrel wall is at the location for the front mount on 6" spacing. If you go to 7.2" spacing by moving the front base forward, the barrel wall thickness is a very serious issue for a good D&T. The obvious solution is to go the other way, and put the 7.2" spacing rear base on the receiver. Problem solved.
As soon as scopes were allowed in matches, Winchester would have made the necessary bases available to the public. I think they started with the 6" spacing. It probably took the military match shooters and coaches a few days to realize the advantage of 7.2" spacings, as time is of an essence in matches. Again, from what I have read and seen, both spacings were being used on '03 match rifles as early as 1914, and I suspect a lot earlier. Both were available in 1916. The 7.2" spacing was used on non-'03 commercial and match rifles even earlier.
Since the width and length of the scope base is determined by the internal shape of the mount receptacle (the part that touches and clamps onto the base), the only variant for any given mount and spacing is base height. So my question is, does anyone know of any set of commercial Winchester bases for mounting the Winchester #2 mount on 7.2" spacing on a 1903 Springfield other than the bases I have discussed?
jt