I dunno about that! It seems to me, that since Apple announced a PCMCIA Card Dock for the Duos and that the Ultra-Dock seems to be designed specifically to house the 1400's PCMCIA Daughtercard with the T-REX PCMCIA ASIC on the bottom of the card cage PCB, it ought to be fairly easy to figure out which of the Duo's full width PBX bridged '030 "slot" signals need to be routed to the half wide PCMCIA Card Headers on the T-Rex/Card Cage. After that, it really ought to be just a matter of hacking the "Dock's" DeclROM to indicate that the PCMCIA Manager is "Present."
This has been a pet project of mine for MANY YEARS now. I used to have shots up of the Card Cage installed in the HDD Bay of a Duo. I intended to use a single height PCMCIA HDD in the bottom slot and a wireless card (with the smallest, most perfect, antenna housing I've ever seen) in the top slot . . .
. . . then I got and then maxed out a 1400c and put the SuperDuoProject™ on hold after falling in love with "Beater's" LCD Real Estate and Heavenly KBD. :