I installed two Micro Seiki 505's, one short, one long on a Luxman TT. I agree, terrific arm choice. Adjustable headshell collet is a welcome feature.
spindle to center of post is it, draw an arc, check your clearances when the dust cover is on, pivot of 77mm long rear counterweight portion, AND check below, you need room for the wide nut and heavy weight below the arm to loosely tighten and finally tighten when setting basic arm height without hitting the side of the base below.
I believe the 62-75 A to B is to position the arm post somewhat 'equally far' from the right side and top, i.e. arc of the counterweight's 77mm length 'centered from top right corner'..
Drill the hole, done.
As mentioned, next position/pivot the arm before tightening for two reasons: tonearm lift, AND to easily loosen the shaft and pivot it to raise and lower the arm height.
Overhang, align the two null points is traditional.
Next, that arm is dynamically balanced, adjust while playing, amazing, read the manual twice!
https://www.vinylengine.com/library/micro-seiki/ma-505.shtml