Appearently there was at least 3 versions, was just looking at a picture of a 1903/Winchester A5 thats supposedly in the Springfield Armoury collection that has the rear block on the reciever bridge and the front block on the barrel just ahead of the rear sight. Sight still has adjustable base attached. This arrangement would give a mount spacing around 9.3'' according to my guesstimations. The picture is in Martin Pegler's book Sniper, A History of the US Marksman if anybody wants to have a look. -VH