[rotorwrench]

The casting marks won't tell much more than what the basic casting part identifier was for the manufacturing process. 1-inch 10-spline is consistent with the transmissions that had the Borg Warner mounting bolt pattern starting in 1949. The late 1951 Mercury used the Borg and Beck 10-inch clutch but a person may be able to use GM diaphragm type clutch from the mid 70s GM products only it would need the modified fingers for the throw out to work. A person can find the L51 Merc clutch on flea-pay now and then. They used the 1-inch 10-spline disk and work well. Ft Wayne Clutch can rebuild them. I use them for my early 51 Merc clutches with the 1 3/8" 10-spline. The cover is almost the same but has a different center hole diameter. I have the Borg & Beck numbers for them in my Hollander Interchange book. A person can also use the 9.5 inch 8BA clutch and flywheel with this spline. Any 8BA flywheel can be redrilled to fit whatever you want. The Borg & Beck or diaphragm type clutches use the same six evenly spaced bolt pattern so that would be the easiest way to go for a 10-inch clutch.