I wish I still had my OG Anvil stem since the Tornado fit is too loose on the integrated stem. It works, but removing the bowl with a magnet can pull the entire oven off the stem in my experience.
Assuming a slightly larger o-ring assembly is out of the question...
I found the USA kit was loose on my 3rd party (futo) stem, which was 1mm larger ID than a stock Dyna (wanted wood for decreased heat build-up; needed a larger I.D. stem to accommodate a TRWW intercooler).
What I did was to leave a little resin build up to help keep the USA on the stem. It works enough to stay fixed to the stem, but I can still remove for cleaning, etc., when needed.
I also use a magnet, but I unscrew the oven on the magnet and let it cool separately from the device. Something I adapted a couple of weeks ago, in order to both cycle slightly faster, and assess condition of the load (I'm a RTL guy, but I do a good job avoiding pyrolization, much less combustion).
Being wood, I suppose one could also use a little 'liquid wood' to build up the mounting surface, but I would definitely research its thermal characteristics first, to ensure no chemical reactions / leaching occur from heating the stack. That would've been my 'Plan B', going forward.