Not sure what you're asking.
The mag chain tension is adjusted with shims - this means that the bolt holes only need to be close enough to assemble. There's no point in trying to get the exact pitch centers, since after the 1st use you'll have to shim the mag anyway for chain stretch.
I have a feeling that some hole elongation to permit rotation around one bolt, or movement through more than 1 plane will help.
If it's too far away, you'll know it because you won't be able to get the chain on. If it's too close the chain will be slack with any shim that fits.
The original timing is done by selecting the 42 gear tooth position (17.14° each) vs. 36 tooth chain tooth position (20° each); 1 ahead + 1 behind = 2.9°, 2 = 5.7°, etc.
If you make an offset key for the mag sprocket, you can use:
1. offset key, CW
2. neutral key
3. offset key, CCW
I suspect that a tensioner could be added to the "hot" (loaded) side to permit minor spark adjustment, but I've never seen one. It could be made externally adjustable (like a primary chain) using the ignition hole for access, and an Allen key on a universal to rotate the tensioner screw on a Teflon "shoe".
Another alternative is to add 1 link to the chain, move the mag farther away, and leave room under the mag to rotate it considerably, using a jacking screw from below with a wedge-shaped block to support the bottom.
With some surgery, a better adjuster could be added from below. Another sprocket is placed in between the chain rows, and is jacked up or down by a screw from the bottom of the case. Jacking it down just removes tension on the chain, but jacking it up rotates the mag sprocket CCW, advancing it. This is an engineering nightmare though, since the extra sprocket must be held in alignment but be free to move on a restricted path with the screw.