I do not know about the sights.  Were they ordinary military, maybe 1901 sights.  The match was held Sept. 7, 1901.  The Irish team had been shooting at long range, various back positions, at Bisley, for years.  I know they shot at 800, 900 & 1000; maybe also at 1100 & 1200 yards. Those sights were pretty standard for Bisley.

There is a guy who lives near Garberville who has one of the Irish rifles, sights and all.  he paid $400 for it 2 or 3 years ago.  I have been trying to get it.   

As far as I know, the only American shooters with a lot of experience at long-range shooting were W. Milton Farrow (been at it since 1874, won the Wimbledon, placed in top 3 at Creedmoor several times, was on the American team that beat the Irish in 1880 and 1883) and maybe G.W. Young.

Farrow would have known about the long range sights and how to mount them, but he was a watchmaker by trade and had already made and sold his own tang sights for schuetzen competition.  He certainly could have made an issue Krag sight into a vernier or click-type micrometer sight adjustable for both windage & elevation.  Fitting custom width & height blades to an ordinary Krag front sight would not be hard.  A sight protector with a hood could be made into a "globe" front sight cover.  My question would be "to mount the rear sight on the rifle butt" to take advantage of the longer sight radius, but shooting from an unfamiliar position or just practice shooting from a conventional prone position.  The American team practiced at Sea Girt for the last 3 weeks of August, 1901.

I have a reproduced copy of "Shooting and Fishing" Vol XXX for 1901, but it is missing pp. 417-478, the part with all the details.