I ended up rolling the dice on a pair of pucks that were going pretty cheap. One is Genius branded, the other seemingly a Genius clone. From the photos I thought they had the same standard sized DIN plugs as the Graphtec, but the photos were deceiving - they are mini DINs. D'oh. I ended up throwing together this little birds nest in the middle so I could experiment with connections.

The puck internals are simple and clearly labelled, which was a nice start.

Measurements on the Graphtec socket didn't offer much insight. There is 2.8VAC at most pins. So I just started working through different connection combinations, focusing on the coil connection to get crosshairs moving. No success at all, so I think I'll need the original puck. I wish I spoke Japanese so I could hit up that Yahoo seller for his spare!

I have learned some useful stuff along the way though. The KD4030B was apparently compatible with the Summagraphics Bit Pad One. I've been down the Wayback & FTP rabbit holes and turned up plenty of old drivers and utilities, but none go as far back as these models. I believe we're looking at mid 70s gear here, which predates AutoCAD by a long shot. None the less I seem to have made progress on the software side, by loading the SummaSketch ADI driver DGSUMMA.COM, and selecting the standard ADI driver in AutoCAD R12. AutoCAD launches without error and displays the crosshairs - so I think I just need the right puck to get them moving.

I archived what I found along the way. There is more Summa support stuff on Wayback that I haven't grabbed as it's for Windows. The download links are all dead, but they give you the filenames to search for.

https://archive.org/details/summa-sketch
https://archive.org/details/sgdosdrv
https://archive.org/details/graphtec-kd4030b-dip-settings

Bonus shot of KD4030B internals:

Thanks, very interesting ! I know nothing about those type digitizers.