I listened in on Charle's zoom meeting last night and I have an additional thought or two. Since you did not build that wing you don't know for sure if the bellcrank is centered. That came up. Here is a quick way since you can't see it. Pull the up line all you can and mark where the down line exits the wing. Now do the same thing with the other line. Pull the lines so that the marks line up. The flaps should be level and if they are, the bellcrank is roughly centered. If they are not, adjust the pushrod till they are. This may or may not be your problem but it is the first thing that you check out in finding it. Once you have the bellcrank centered, mark the leadouts and use clamps to keep them from moving as you make other adjustments. Plan "B" - get a small camera snake and peek in through the exit hole in the wing.
Now, make yourself a tool to lock the flaps level. I would use a piece of hard foam or soft balsa cutout you could slip over the flap and lock it level. With the flaps locked level you should not be able to move the elevator more than about 1/4" up or down including slop and it should be level to start. From this point forward only use the flaps to adjust for roll. Regardless of what you think, if the CG is correct, the flaps will center themselves in level flight. Adjust the elevator or maybe the thrust line. The last thing you do when finished is adjust the handle for level flight. Asymmetrical line spacing is an absolute last resort.
As you move up in skill the accuracy of the adjustments will need to increase but the end result stays the same. Your top experts could tell you if the turn rate was off by a foot or less.
Getting a 60's profile to fly like a modern PA is never going to happen but you can get close - Good Luck - Ken