Just for information.
The original sidestand on my '74 450 MKIII has a length from the centre of the sidestand pin to the base of the foot of 280mm (11"). On soft ground, or gravel, I put a thin (3mm) plastic puck beneath to prevent it sinking.
In the workshop I sometimes level the bike up a bit by putting a piece of 95mm x 45mm (4" x 2") under the stand and this gives a length from the pin centre line to the ground of 325mm (12¾") that appears to be similar to the measurement that you give for your stand. This does make the bike more prone to be toppled, even with the front wheel turned to the nearside.
Maybe removal of 45mm from the arm and then pin and reweld the standard foot back would solve the problem, if you cannot find a replacement MKIII sidestand. Adding length/distance between the side stand arm centreline pivot and the ground surface,
will just exacerbate your problem."Is there a solution, other than carrying a hockey puck around with me?"
I can measure the side stand pin OD if you wish, or post images to show the angle of dangle from the front and rear, if necessary.
Good health, Bill