Hi Guys
I'm not going to be lotta help. NONE of my '60s or Open Top guns have OEM sights. They all have brass dovetail sights, filed more or less to hit center on a typical 14 x 14 CAS target. Since I seldom, if ever shoot at paper anymore, I consider "minute of Pie Plate" an acceptable "group." I do try to put the front sight on the lower third of the targets though, as I have a tendency to "climb" the targets when shoot quickly.
Were I to try to shoot for group with open OEM sights, the "hold" would be at 6 O'Clock with some form of aiming point for reference. As long as I know roughly where the point of impact is in relation to the sights, I'm good.
As an additional, with ANY open top design revolver, until the Barrel to Arbor fit has been corrected, trying to get a group is a waste of ammunition and time. If it's a Uberti, out of the box, the Barrel to Arbor fit has traditionally abysmal.