Hey, sorry to keep bumping this thread with extra posts!
I took the liberty of posting this in the Self-Made Keyboards in Japan Discord, to double-check the JIS kitting, and they pointed out one issue which I'd missed. In the number row, you have a "0, わ, を" key for the hiragana sub legends version, but no "0" key for the latin mono legends version in the row below. This is necessary because if you try and use the standard ANSI 0 you'll end up with the top legends being "(", ")", and ")" for 8, 9, and 0 respectively, with two right parentheses.
In a JIS layout, there is no punctuation symbol above the 0, and with no kana sublegends, this means that the key will have only the single legend "0". The usual thing to do here is to align it the same way as the rest of the numbers, so in this case it would go at the bottom-left.
Here's a pretty representative example.