i just happen to have one, new in box! i bought this years ago at Weird Stuff Warehouse when they were still around. i have no idea why, but i'm glad i did.
looks like it is essentially the same protocol as the version of the mouse (type 4?) designed for the SPARCstation. the output is open collector, inverted async serial, 5 byte.
time to build an adapter. the connector is RJ11 (technically 6P4C) but it has these pins sticking out, presumably so you can't plug it into a phone jack.
four months later i made the Video Snake Oil board that can adapt 13W3 (any type!) to VGA. you just wire up the little pads to whatever your machine needs.
i've also installed a ZuluSCSI. this neat little board is a lot cheaper than a SCSI2SD. i'm going to try and install Solaris using a CDROM ISO file. CD6_512.iso is placed on the SD card. it'll be ID 6, 512 bytes per sector.
@thejpster@tubetime One of the quirks of the early sun machines is a reliance on 512-bytes-per-sector CD-ROMs. It’s not as impossible as it sounds, because many of the contemporary SCSI CD-ROM drives also support a mode select command to enable it.