eientei posted this video link on Discord. Now, let's not get our hopes up of this ever getting this emulated since it's super rare, but it's cool to know that a G&W Tetris prototype really does exist.
Clamshell model here is JB-63 (safebuster). From the number of segments used, I'm guessing it's SM512.
*edit* mixmaster posted this on shoutbox: https://www.asahi-net.or.jp/~ua4s-njm/gw/gw_ms16.html and the description there matches that video, talking about the scrolling playfield and clowns
