The quick easy fix with a pic rail is to use some new Burris XTR Signature rings.
https://www.burrisoptics.com/mounting-systems/rings/xtr-signature-rings For a more professional fix I would pull the barrel and verify and correct the direction of exit curve in bore. It's a lot more likely the curve is what you are up against. On a custom rifle the curve gets timed straight up and then when you sight in the rifle most of the time the scope only needs a click or two at most from optical center.
When converting an action to 8-40 you should pull the barrel and mount the action in a fixture and then dial in the mill to mill the new holes perfectly straight with the bolt bore raceway using an end mill based on the blueprint rather than the old holes. I personally like to put off enlarging the holes until the 6-48's are no longer feasible. There is virtually no structural strength to be gained with the larger screws due to less threads being utilized. It's about 1 full thread less holding per screw. Running 6-48's is about the same as using 5 screws instead of 4.
