Machining 1/8 off the pulley mounting g surface may weaken the pulley.
I think that the trigger wheel could be machined to fit a set spot on the crank pulley by the balancer.
I don't know what type of equipment is available to you....but...if there could be a lip machined on the back side of the trigger wheel it would serve as a spacer from the balancer and a mounting point.
It could also be a...let's say...3/8 ring that slipped at the bottom of the stock crank pulley. The ring could be drilled to take #7 Allen head bolts with nylon lock nuts ( inside the crank pulley. That trigger wheel could be drilled with slots that allow degrees of movement with allen screws, flat washers, and lock washers to secure. The machined ring would just need to be tapped to accept the allens.
It wouldn't be hard to make a template for drilling the holes in the balancer.
The balancer ring would also serve as a way to ensure its placed on the correct spot. Lay the ring down on a flat surface, set the pulley in the center and mark. Lay template using one of the pulley bolt holes for reference, center punch, and drill.
The crank pulley should be centered by the lip on the front of the balancer.
The balancer, center hub, is machined. The crank pulley inner hole is machined....so the only place for error is if the stamped stock pulley has wobble in it.
The other option to nullify that is a machined aluminum stock diameter pulley....
That would take out virtually any wobble... Since all surfaces would be machined.
Just an idea....
Edit ; I started this post at 10 am....since then I now see what type of stuff are available to you....that trigger wheel looks awesome.