Jason - not sure about the c-163 you found in the distributor, but the other two are the GM casting or part numbers for the engine block and the intake manifold. The good news is that both numbers are correct for a '73 small block.
If you look a little closer you will find a few more letters and numbers on the intake right near the 7771 number. It will be a letter and a few numbers that tell you the casting date of the part. My intake which is the same P/N as yours has a L52 cast into the intake indicating it was made on Dec. 5th, 1972. (A= Jan., B=Feb., etc.)
The same type of casting date can be found on the engine block in a similar position you where you found the 0010 casting number only its on the passenger side towards the top of the block. My block has an L42 casting date indicating it was made on Dec. 4th, 1972.
Your question regarding the originality of the engine starts with numbers like these, but the defining piece of information can be found on the flat surface or pad on the top of the engine block just below the valve cover and in front of the passenger side head of the motor. Here's a shot of mine, pretty grungy because it was taken the day a bought my car and one of the first things I checked before buying it.
The first nine smaller digits you see are the same as the last nine numbers of the VIN of my car. They were stamped there in the factory to match up with the frame and body stamped with those same numbers. Those are the first indicators of a "numbers matching" or original engine, but that is just the start.
In addition to the VIN numbers you see the larger digits of V1206CLR. V1206 indicates the motor was assembled in the Flint MI. plant on Dec. 6th. Small block C3 motors were assembled in Flint, Big block motors were assembled Tonawanda NY. and have a T as their first digit. CLR is the engine suffix code indicating 350 cu. in., 250 HP, mt - which is the correct suffix for my car which is an L82 4 speed.
So now you have the beginning of a very long story called "numbers matching". First - does the VIN on the block match the last nine of your VIN number and title ?? Does the engine suffix match up with the engine and transmission options of your car ?? And third, do the dates line up. Where the parts cast before the engine was built ?? It's a little hard to have them cast after !!
The story continues with many addition parts of your car. The last nine of the VIN is also found on your transmission case. Like the engine, it is the first indicator of originality. Many part number's, casting dates and other date codes are part of the story.
Take a look at your motor, clean the top of the engine pad and read the numbers stamped there. Hopefully you will find the right information to start you off. A base motor 350 with automatic, non-California emissions should CLA engine suffix. Hit the internet and you'll find lot's of information on the rest of the numbers matching story. You can also find much of the same information contained in the posts of this forum by using the "search" function. Let us know if there is anything you get stuck on.
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John Sigmund
valkman57@sbcglobal.net
NCRS Member 61302
NW NCRS Chapter Member
Duct tape is the new Black !!