Japanese JIS layout has a long left Shift and a vertical Enter key, but it also usually has a 1u Backspace, a smaller right Shift with an extra 1u key next to it and a few extra modifiers for Japanese on the bottom row next to a shorter Space Bar, often with the Alt and Win modifiers squished into smaller keys than otherwise.
Building a GH60 (60%) would be possible without any plate, as it supports PCB-mounted stabilisers.
The Phantom (tenkeyless) supports any combination of ANSI and ISO, windows keys or not on the PCB, but you would have to get a custom plate made. (BTW, the Phantom does not support JIS...)