This is what I found when I was restoring my 1978 case 220 lawn tractor.
Step 1: Start
What I found when I started restoring my tractor. looks like old push rod wore down and that was their fix. The tractor would not run.
Step 2: Find and Grind
What I found around the garage was a 6 inch Ollie lag screw (hardened steel) I cut mine an inch longer then what I needed. I then used a drill as my lathe. alternating between a file and sandpaper checking the fit every couple minutes.
Step 3: Polish Smooth
Using a light cutting rubbing compound and a piece of OOOO steel wool. still in the drill spinning at a high speed polish to ultra smooth. make sure there are no burs. The push rod must be loose enough to move but tight enough so as not to let oil leak out.