Only a guess but because these dampers were designed by test rider "feel", the small holes might have been put in to reduce the damping when under hard braking since they do not have the pop-off valve of modern dampers. I think you would be better off replacing the dampers with something more modern that can be tuned.
Vintage rules here allow up to 38mm forks. I would look at that route. Search on line for "motorcycle fork diameter list" and there are lots of 38mm forks to chose from. Pick a road bike used for racing made for a large range of years such as the FZR-600 89-97. Those would likely have good dampers already.
Modern forks typically have a separate damper tube for the head to slide in rather than the fork tube itself. This allows for a closer tolerance without having to hone the stanchion itself. It also is not affected by the slider/stanchion clearance or bending of the stanchion.