I did have the 8th Illinois Cavalry south of the Fairfield Road just minutes prior to 4 p.m., but it appears to me from the following that the 8th New York and 3rd Indiana were posted north of the road.
Sources:
-I immediately rushed Gamble's brigade to Doubleday's left, and dismounted it in time to render great assistance to our infantry, and to check and break the enemy's line. My troops at this place had partial shelter behind a low stone fence, and were in short carbine range. Their fire was perfectly terrific, causing the enemy to break and rally on their second line, which made no further advance toward my position. (Official Report of John Buford)
-An hour before dark the rebels outflanked our left, this brigade of cavalry was again ordered to the front, dismounted, and fought the Rebels on the Seminary Ridge and saved a whole Division of our infantry from being surrounded and captured - nothing of this either is mentioned in the newspapers or dispatches, yet these facts occurred with the loss of some of our best officers and men. (William Gamble, letter of March 10, 1864 to W. S. Church)
-In the afternoon the enemy, being strongly reinforced, extended his flanks, and made a desperate attempt to turn our left. They advanced in three strong lines, when our brigade was ordered forward at a trot and deployed. Half of the command was dismounted and placed behind a portion of a stone wall on a ridge of woods, with the Seminary on our right. The enemy being close upon us we opened an effective, rapid fire with our breech-loading carbines, which killed and wounded so many of their first line, that after a short heroic struggle to continue the advance, they could stand it no longer and fell back on the second line. Our men kept up the fire until the enemy, in overwhelming numbers, approached so near that in order to save our men and horses we were obliged to mount and fall back rapidly ... (Col. William L. Markell, 8th New York Cavalry, New York at Gettysburg, III:1145)
-Late in the afternoon ... my command and the 8th New York were ordered to check the advancing columns of the rebels ... We took position, dismounted, along an old stone wall to the left of the Theological Seminary, along which is a thin skirt of timbers and held our position until we were flanked by the enemy. Although but a short time in this position, we so checked the advance of the enemy, as to enable a division of the 1st Corps to pass safely through the town ... (Col. George H. Chapman, 3rd Indiana Cavalry, Bachelder Papers, 1:130-131)
-... the four pieces again retired, and took position upon the ridge running south from the brick Seminary, and in rear of the belt of timber to the left of that building. ... the enemy charged upon the guns, the four pieces again retired under cover of the line of cavalry already formed to cover the withdrawal of our troops. (Official Report of Lt. George Breck, Battery L, 1st New York Artillery)