So…. i found some more details around this, in particular that confirm that 'cabin blower' is indeed a term used for cabin pressurisation pumps.
I also found some pictures of the Marshall 'cabin air pump' or 'cabin blower' or 'cabin superchargers' like that fitted to the Spitfire
The Marshall unit looks similar enough to the Rotax unit i have, that combined with my recollection of it being described as a 'cabin blower for for a Spitfire' makes me think that it is a cabin blower for something, just maybe not a Spitfire.
The search goes on.