Jack, The last Savage catalog to actually picture the Lyman sights was No 50 (~1912~) and it still has the same picture as all the earlier catalogs, I looked at a number of newer catalogs and no pictures, trying to find the time of the change in Savage literature appears to be a dead end. The Lyman sight with either the 'ring' spring or the locking feature proportionally cannot take as long a stem as the design used for the No 18 & No 19, so either of those newer designs would require the sight to extend back farther on the gun to allow it to be tall enough to have a reasonable adjustment range, this may be why they stayed with the original design for so long. The same basic design used for the No 18 was used for the Remington pumps and the Winchester 61 - as far as I know these were the only option Lyman ever offered - for these to be able to mount a taller sight the base would have to extend back a few inches and would not be very practical.
To find a time when the new design was offered for 1899's you will probably need to looks at Lyman catalogs or suppliers catalogs - maybe Stoeger's? if someone has library full of them.
