First, a question for you. Is the front sight blade on your ROA replaceable? If so you can fabricate a taller replacement blade. This will cause the shots to hit lower on the target. You can then file the blade to raise the point of impact to the point of aim. If you can't replace the blade, you can try making and soldering an extension to the top which will serve the same purpose.
To correct for the windage error I suggest you contact Ruger and ask if they have any recommendations. Even though they no longer make the Old Army, I am sure they will be happy to service it.
Should Ruger not be able to help your situation, you can consider thinning the blade by filing it on the RIGHT side. This will have the same effect as moving an adjustable rear sight to the right. Note the old advice of moving the front sight OPPOSITE the way you want to change the point of impact does apply in this case since you will be moving the centerline of the sight (by thinning the blade on the right side only) to the left. It shouldn't take much metal removal to change the point of impact by the desired amount.
I hope this explanation is clear enough for you. Sometimes it is hard for me to put concepts into words. If you have any other questions or if I've confused you more (I hope not), ask again. I'm really surprised you haven't already gotten a bunch of advice from the guys who usually post here. There are some really competent people who contribute to this forum. Good luck!
