Jason,
This is an MP-50 mount, second war vintage but used throughout Korea and VietNam. If you are after a mount for either the 442 or 151 you can use the standard sugar scoop. I don't have the number handy but the mount you want is s similar in shape to the AB-450 but has tapered sides where the AB-450 doesn't and won't fit on the side of the 151.
Kurt
KG6KMJ