Hi Ross,
Glad you're getting the threading under your belt. It'll still bite you now and again... Well it does me!
Looking good on the engine front.
Flywheels are notoriously annoying to cut out/ trepan or what have you...
You might find it easier to build one from 2/3 parts?
I'll pen a C-o-C for you to help explain


Does this make sense?
You make a displacer disk (bottom bit) and then the 3 parts of the flywheel are assembled with a smear of loctite (the .9 measurements are to show a smaller fit... Might need to be nearer .6 to allow for easy assembly?)
Anywho, loctite the outer edge of the disc and the hub. install onto the displacer disc and lower the outer ring over and make sure it's all flat (I'd assemble on the surface plate.... There should not be enough loctite to drip down. And it can be wiped up easy enough)
Leave over night and then it should have bonded well enough to be able to drill the centre hole (using soft jaws if you have them? for greater acuracy. )
You could make it in 2 parts but the hub is easier to make and bond I'm thinking!
As long as the bits are a sliding fit and you have a reasonable strength loctite it's a relatively easy way to make a flywheel

Hmmm... Thinking about it you could even machine a micro step in the ring (at 6.5mm in this drawing and it's sizes) and centre so the parts sit to a shoulder?
Cat skinning and all that!
Hope that helps? I'm sure someone will go into the trepanning side of things?
If you need any further things to be drawn out, over complificated and long windyfied just ask
Ralph.