I'm familiar with them, and not sure they're relevant.
Upshot is that so long as 922(o) holds, the feds can't bust you for not paying the $200 tax on a post-'86 MG ... but you can still be busted for violating 922(o), which is harsher. The rulings simply do not go any further than that; they do NOT invalidate any part of NFA law which is not shadowed by 922(o).
...and...
Should 922(o) be overturned, the parts of NFA it covered would be restored.