With regard to the registering of the flywheel on the spigot of the crank flange...
This picture shows that there's not much room:
View attachment 1716208017
Just a tad under 6mm, so then what's the thickness of the Quicktime balancer? I can't see it being less than 2mm, possibly 2.5mm, which is still less than ⅛" (3.2mm). And then there's the chamfer on the bore of the flywheel, which I couldn't measure:
View attachment 1716208019
This might well steal away another 2mm, but even if it's only 1.5mm we're looking at less than 2mm of the outside section of the spigot providing a secure seating of the (heavy) flywheel.
