SewerSleuth,
If you are writing at me, it appears you didn't fully read my post. Your biggest complaint was the gap on the top of the platters. This shim doesn't correct that.
This shim isn't just for the Karousel. When I was a Linn dealer in the 1980s, there were LP12s then where the outer platter rode high. This isn't a new issue. This shim should work on any LP12 since the screw holes are in the same place and the Karousel has the largest diameter bearing housing.
It is probably just a cosmetic issue, though it would definitely make even more contact with a Valhalla board. It may even cause an issue with other crossmember versions.
Can you please make a before and after recording. To be clear, you will need to lower the tonearm height, reset the springs, and adjust the P-clip & tonearm cable length. I suspect your LP12 will look slightly better but perform slightly worse.
The good news is you can return it to unmodded use.
Ron The Mon