This is a photo of spacers that were installed on the leading edge of the RH front door frame in our MK2. The rear door frames utilize the same spacers. I purchased a one foot length of nylon rod from McMaster-Carr and cut and drilled individual spacers to get my margins close. I then used individual body mounting washers to achieve my final door frame to seal margins. As you can see, there’s quite a bit of room for adjustment (more than 1/2").
As Tapped pointed out, the mounting brackets can rust and fail to hold the base of the frame in place. Our MK2 is also a California Black Plate example and I had to repair the RH rear most mounting bracket. Lastly, check the state of your frame. The brazed joint located at the rear window frame where it meets the door top mounting cross piece failed on our car because the bottom bracket failed which allowed the frame to twist and fatigue the joint.