I can imagine that they were AC instruments? Made by The McKinnon Industries Ltd in St Catherines?
As to production, I cannot recall any evidence of Sunday working. Up until the end of June 1941 Regina were producing vehicles but then went over to munitions solely. However Windsor Transmission Plant and the Motor Plant in Walker Road, and the Oshawa Plant were producing engines, gearboxes and vehicles. Up until February 1942 Oshawa also assembled civilian vehicles. If there is anything about shifts it might be in the newspaper cuttings from THE REGINA LEADER-POST which is all I have that refers to actual working habits. The local Oshawa paper might have details say of accidents which might indicate working days. I can imagine that Sundays were devoted to care and maintenance.
That all said I have been asked about production ramping up. Years ago I was treated to Xerox copies of info from McKinnons on engine and CKD production. These are a mine of info if you study then analytically. However I just don't have the time right now as I am blasting out articles for the magazine. That is why I thought I would post decent copies online for all those interested to have a look and see for themselves. The Windsor motor production figures would have included engines for civvy vehicles, for Regina and spares of course, and the CKD production included MCPs as well as CMPs. Anyhow, here are two LARGE files and hope that they help.
http://gmhistory.chevytalk.org/ckdproduction.jpg
http://gmhistory.chevytalk.org/motorproduction.jpg