You have a Muncie transmission from a very late 1966 Chevelle that was assembled at the Atlanta, GA plant. 6A188393 is the partial VIN of the car and P0701 is the assembly date of the transmission (July 1st, 1966). It "could" also be from a full size car since Atlanta built both that year, but I think by July, 1966, full size cars would have been WAY past 88,393 built. I'll verify this with Warren.
How many rings on the input shaft?
Ed