There is a soft plug behind the cam in the space behind the flywheel.
You could take the soft plug out to avoid pulling the cam but that seems
to be the hard way. You'd have to replace it with a new one.

Do you have reason to think the cam has been replaced? If not, post the
engine number on the side of the block above the dipstick (2 or more cast
digits, the rest stamped) and we can probably find what kind of engine and
thus what kind of cam it had originally.

The vast majority of B18s and carbureted B20s had the C cam. Early FIs had
the D cam and later ones had (I think) the slightly different K cam.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma