This pushrod trick in the intake lifter hole will not work on the "Big Block" engines such as the 120, 150, 180, & 220 engines for they have "mushroomed bottomed" lifters that cannot be installed or removed with the cam in the holder.

On these engines you hold the cam gear in position with an Exacto blade jammed into the gear teeth on one side while you insert the cam assembly onto the crankcase.

I have just free handed the timing and then checked myself with the above mentioned "overlap" method.