The recollection (by Ralph Bootman - but just heresay at the moment) about initially using a factory from the old Norman and Beard company is consistent - the linked history identifies that firm as having somewhat extensive buildings on St. Stephens Rd, which was just to the west of Timberhill St. It sounds like that general area suffered much damage during 1942, so I guess that recollection would also be consistent with Osborne Buildings which would seem to be just a bit to the NE.
http://moothallorgan.co.uk/history-of-norman-beard-ltd/
I can't locate Osborne Square on the 25 inch map below, but it seems to be west of Farmer Ave (perhaps between Timberhill St and Farmer Ave). I don't have access to your reference sources - are you confirming that "Osborne's Buildings" was on Osborne Square?
http://maps.nls.uk/geo/explore/#zoom...layers=168&b=1