Best to find a new, not rebuilt, remanufactured nor NOS fuel pump exactly for your motor and year.
While all early chevy fuel pumps will bolt on, not all have the same type lever and it's action matching a particular cam - there have been changes over the years. You can end up pumping too little or too much fuel or in the worst case break parts inside a pump that doesn't match.
Regardless of what the box or label says, compare the lever and it's action with your original one.
To make sure the pump fits, rotate the camshaft until the fuel pump lobe is at it's highest point and check that the fuel pump lever does not bottom out before it mounts flat against the block.
The inlet and outlet orientation depends on the differences between truck and car vacuum advance and road draft tube types.
The top of (and bottom of vacuum assist) fuel pumps can easily be interchanged regardless of years.
The important thing is the lever matching the cam lobe.
