I imagine if they machined a circular insert that would slide in and reduce the diameter of the hole slightly, you could adjust the stands to fit the VR carb cap perfectly.
Yeah the dish isn't needed at all for the flower. Although it's pretty hard to break a small piece of quartz. You could also opt for the SiC dish, which feels somewhat more resistant to breaking. Either way the dish is only used/required for dabbing purposes.
I got mine from : https://www.swissjewel.com/products/balls-hemispheres/ruby-balls/
For some reason their quartz balls are more expensive than their corundum (sapphire/ruby). I would have guessed it would be the other way around.