Martin- I used to post on a Clansman site, hoping to get in touch with old workmates, but no luck. I've lost the site as I've had no contact. Might be worth a Google on Clansman 353 or similar. Possibly this site?
http://www.clansman-radio.co.uk/history.html
However, I've found a manual online. Perhaps somewhere in there are dimensions.
http://www.ferret-fv701.co.uk/radio/...escription.pdf
And after a search, I've found that Warrington Radio club have a section on the 353.