Econet for an RML380Z?

Has anyone ever seen (or heard of) an RML380Z with Econet network support (rather than the usual coaxial that RML used for its CHAIN network)? I picked up an SJ Research MDFS Econet fileserver the other day which I'll have running at the museum. However, the docs at one point (and one point only, it seems so far) mention RML380Z fileservers and 380Z machines with Econet. (I've got an RML380Z fileserver, but naturally it has a CHAIN network board and not Econet!) As I collect Torch, Acorn and RML stuff (and Torchnet is at least electrically compatible with Acorn's Econet) it's of particular interest as it implies one day I might be able to connect machines from all three manufacturers. I've never seen mention of Econet support in any of RML's documentation though, so have a feeling it was maybe a product that never saw the light of day... cheers Jules