I have years of experience in crawling through Canadian Archives, Canadian War Museum and DND historical records. Not once did I see anything remotely resembling the Valentine drawings. However, I did find the 30-odd volumes required if you wanted to set up a shell manufacturer for Naval gunnery.
Typically, these drawings would have been held by the Department of Munitions and Supply as DND was only a customer for these tanks - they were not involved in the design specs in any way. Unfortunately, the DMS archived files are still not properly accessioned and it may be years before Archives gets around to doing this, assuming that the Valentine drawings still exist. There is a real possibility that the Angus plant would have held onto these and then disposed of them when the last Valentine rolled through the doors.