Windsor oil system

[ajmac]

Great manual drawing George.
That shows that the Windsors had a good filter system, probably the best in wartime for flatheads. There is a plug inside the block isolating the oil feed from most of the engine, thus oil goes via the TCV through the cooler and what looks very much like a filter casing before returning to the main oil rail. On flatheads the rear main bearing and a few other bits have oil supplied from a gallery connected directly to the pump output, thus this oil can never be cooled or filtered. Also looks like the filter is only in use when the oil is warm, hey, better than nothing! If you have the arrangement shown in the drawing, then with very hot oil you have 95% filtration, not a bypass system, you can't get 100% filtration with original wartime components.
Any chance of a photo of your Windsor, I have not seen one up close.