The Budd Company produced Rail Diesel Cars in five basic configurations: 

The RDC-1 - an all passenger coach with seating for 88 passengers.

The RDC-2 - a Railway Post Office (RPO) and passenger coaching seating 71 passengers. 

The RDC-3 - a Railway Post Office, baggage compartment and 44 coach seats.

The RDC-4 - a Railway Post Office and baggage compartment and no passenger seating.  The RDC-4 was 65 feet long as compared to 85 feet for RDC-1,2,3 and 5 designs.

The RDC-5 (or RDC-9) - an all passenger coach with seating for 82 passengers.