It's a lot trickier on a shaft mounted rocker system. Pushrod length does not change the pattern on the stem. That's changed by raising the shaft stands up or lowering them down.
Here's what you have to look out for:
The adjuster in the rocker arm needs to be choked up pretty close to the rocker body. Close enough so that it doesn't put a bending force on the adjuster, and so that you don't get a big arc of movement as the valve opens. It needs to be far enough away so that the cup of the pushrod doesn't rub on the rocker body and so that any oiling orifice in the rocker arm hits the adjuster and pushrod cup in the correct way so that the adjuster gets
oil.
You didn't mention what rockers you have or if this is a hydraulic or solid cam. Those things will also dictate how you determine pushrod length.
You also didn't mention if you have a regular ball/ball pushrod length checker, or if you have a ball/cup checker. Trend usually wants a BOC (bottom of cup) measurement, and there are several ways to get that.
If you tell me what checker you have, what rockers you have, and what lifters you have, I can tell you exactly how to determine correct length.