The 1966 tags DO NOT have a complete VIN on the tag!!! What you see is the first four characters, which signify what the car is. RH27 is a Belvedere II convertible. The H4X is the grade, material and color of the INTERIOR, and has zip, zero, nada, zilch to do with the VIN. That means it has a High trim level (H) bench seat (4) interior in Black (X). Complete VINs on a fender tag started with MY 1968 cars.
You probably have a 383 car there, judging from the 383 emblem and the "G" in the VIN tag.
What you are seeing in the VIN as an "A" is probably a "4", which is the build plant, which in 1966 was Lynch Road. SS1 is Cream body, Cream painted top, and 1 means Monotone paint. But since it's a ragtop, the second "S" has no significance for this car.