That's Classic's number for Layson's mount that they resell- Layson's number is RD-636SCSI.
But he lists it through '69, which ain't right- should just be '64 through '66.
I still personally prefer to use the truck biscuit I referenced above. Especially with anything that has a warmed-up smallblock, since it has a built-in torque limiter and is the correct height.