Showing a couple different versions of a pushrod removal/installation tool for Mopar 318 A-block. Removal of the rocker shaft is not necessary.

Info on the poly engine...
https://poly318.com/poly-318-engine-h...
"Many people throw around the term “poly” as if there was only one type of 1950’s Mopar engine family with polyspherical heads. What we call the “poly 318” is the A-block family that includes the 277, 301, 303, 313, 318, and 326. All factory A-blocks have polyspherical heads. The confusion stems from Mopar having multiple 1950’s V8s that use the Gen I Hemi block with polyspherical heads including Dodge (also used in some Plymouths) 241, 259, 270, 315, 325 and Chrysler 301, 331, 354. (DeSoto never offered a hemi-block polyspherical head engine or an A-block). These Dodge and Chrysler engines are typically referred to as “polys” or “semi-Hemis” but are extremely different from the A-blocks with almost no parts interchangeable. I find that using the “A-block” and “Hemi-block” distinctions clears up the “poly” confusion."