GM RPO build codes

Almost every mechanical part made for a Chevrolet has a date code, either cast or stamped into it. These simply identify when the part was made. To the factory, this date probably made sure that they didn't leave any stock laying on the shelf too long, although if you have ever watched any factory production line run, it is doubtful if anyone ever reads the dates. The purpose of the date to Chevrolet was probably to ensure a means to track any defects should they arise. If a part dated March 3 and one dated March 21 were both defective, attention could be paid to those parts built between those dates for other possible defects. Today, these are used to determine if the part is correct for that Chevrolet , as an engine with a date code of D 16 5 (April 16, 1965) could not be correct for a '63 Chevrolet as the engine was made after the car was made. Parts too early are usually not correct either, as they would have been installed on an earlier vehicle, such as a B 23 3 (Feb. 23, 1963) in a '67 Corvette. NCRS provides a window of 6 months on date codes prior to the build date of the car. Obviously, a part on a car could not have been made AFTER the car was made. But given how new items were constantly loaded on shelves, with existing items being shoved further back each time, a part could sit for many months before being assembled on a car. Usually, the parts were used within a few days or weeks but there are many documented original cars that have parts several months old. Be sure to notice that some parts have both a casting and a stamped date code. These can be several days apart. The stamped date code is when the part was assembled and should be the one considered.  

'''Engine Block:''' The date code on a SBC is typically on the bellhousing flange behind the distributor. On early big blocks, it was on the passenger side near the pan rail, but later (1970) moved up to the same location as the SBC. Usually the date is given as a letter, a number and then a number, such as B 23 3 which is for February 23, and a year ending with "3". With any engine still having ignition shielding on, you have a very hard time to see the date. A good flashlight and a wire brush to clean any dirt are a must, even with the shielding removed.  

'''Carburetor:''' Most of the earlier carburetors were built by Carter and had an identifier tag attached to a cover bolt. This tag had the part number and date code. On Holley carbs, the List Number is stamped on the drivers side air horn in front along with either a 3 digit or 4 digit date code. The Rochester QuadraJet has a stamped number on the driver's side on a vertical pad on the secondary casting of the carb body.