Look at your photo of the booster- - - - -that looks a lot like a bolt and a lock nut where the plunger pushes the master cylinder. Dimpling the adapter accomplished the same thing, but in case you need to make any further adjustments, you can fine tune it in either direction without doing any more drilling.
Jerry
Yes, I tried to adjust that first while my wife patiently held the MC so it wouldn’t bend the brake lines. No matter what I did, it didn’t seem to change the booster rod tip length. So I resorted to drilling the spacer for the same result.
