CMP Chev master cyl.

[Grant Bowker]

Bob, I am sure that my C15A and almost certainly yours have the mounting studs for the master cylinder staggered on the base of the casting rather than on the side as in the ebay listing.

Based on an old Wagner parts Catalog, a possible interchange might be their FC-4388. It is the correct style of mount (according to my statement above), 1-1/4" bore, stated to be for General Motors vehicles. They give the stroke as 1-7/16" but I have no way of telling if this matches the spec for the Chev CMPs.
The Chev M/C, part number 5450260 (does not appear in the cross reference section of the Wagner catalogue), is listed in some (but not all) CMP parts lists as "*" or "peculiar to to Canadian Military Pattern vehicles" but I have no idea what makes it "peculiar".