Small Block & Big Block Chevy Specific - Valve lash problem/rocker bottoming out

Alright, I'm helping my buddy assemble his 350. I bolted on the new heads and installed his new cam. I have an adj pushrod and a test spring.
The problem occurs when I try to measure for the correct pushrod length. After adjusting to get the wipe pattern progressively towards the middle of the valve stem. As soon as I adjust the pushrod to get what i think will give the perfect wipe pattern...I try to set the valve lash on the rocker before turning over the motor and the rocker bottoms out on the head before I can get the poly lock tight. :confused:

These are somewhat bulky extruded aluminum 1.6 SA rr's. I don't recall the brand, but they are under 200 bucks, so I know they are cheap. I was thinking that the lifters might have bleed down a little so I primed the engine using a priming tool and got oil coming out of all of the pushrods, but still have the same clearance issue. Has this ever happened to anyone before? I might also try to get a hold of a different rocker like a Comp Pro Mag to see if the wipe patter is perfect with the pushrod length that I am trying to use.

You might need to shim the rocker.

You might need to shim the rocker.

How do you shim a rocker?

if they are hydraulic, they will more than likely bleed down. you don't have to turn the motor over to get pushrod length. set the PR length checker so that it's just offset from the center of the valve tip towards the intake side of head. So when it is on full lift, it will be in the center. hydraulics are usually done this way because of bleed down.