Well, that'll teach me to rely on alpha code for my day-to-day computing... I switched from kernel 2.4-test* and the alpha NinjaSCSI driver back to kernel 2.2.16 and the more-stable NinjaSCSI3-1.0.2 driver. Success! I just finished an X-CD-Roast session.
The Panasonic KXL-RW10A now works (in 16-bit mode) with my Mitsubishi AMiTY CN2 (TI 1220 controller, Slakware 7.1) and my wife's NEC Versa 6050MH (TI 1130 controller, Mandrake 6). I was even able to squeeze the nin_cs.o module onto the Slackware pcmcia disk image so that I could install Slackware from CD.
Thanks to everybody for your helpful responses.