It's possible to wire up an adapter that lets you
use a ZX81 (or was
that TS 1000?) RAM pack on a Jupiter ACE ... I've seen one such working!
The TS 1000 and ZX-81 16k RAM Packs are identical except in
their markings.
Jeff
--
Collector of Classic Microcomputers and Video Game Systems:
Home of the TRS-80 Model 2000 FAQ File
http://www.geocities.com/siliconvalley/lakes/6757