Pics didn't post through jason.
If the carb is original to that motor and it's truly a '73, then the IH p/n should be the first line stamped on the front of the air horn, right hand side facing the engine. Second line May say "list" followed by a four digit string with a suffix (maybe). Third line is date code and is not important at all.
The list number is what is important.
If there appears to be a "stick-on" label on the air horn or body, that indicates some kind of commercial reman, hopefully there will be a number string printed on that. If it is a reman, then that number is what is important.
I can tell ya what it's had oem, but that doesn't matter with this old stuff, what does matter is what you have and need parts for.
Try again...and take a flashlight and shine at an oblique angle on the air horn to make the numbers stand out.