41 Chevy,
Sorry I didn't do this sooner. In
THIS PHOTO, which is a '41 216, the main oil gallery is the "ridge" that runs from front to back, about halfway between the manifolds and the oil pan. Behind (to the right) of the exhaust tube, and just to the right of the curved copper oil line, is the oil pressure line hookup into the main oil gallery. You can just make out the line running up to the cowl for the gauge.
As long as your engine is a '41 235 (not the later-model 235 with high-pressure oiling), yours will be the same.
Does this make sense and sound right to you?

Hope it helps,
-Michael