The pushrod length is not going to make an difference on your P/V to valve clearance, at least nothing notable. You can check P/V clearnce with what you have there now.

All I have right now is just the wimpy checking tool (I don't have a set of checking springs). I do have the adjustable roller lifter so I was going to use that with the new pushrods when I get them and check the PV clearance and wipe pattern on the valve stem tip. I'm not sure how to check the PV clearance without a real pushrod or swapping in checking springs. I would be afraid that the pushrod checking tool would bend under the pressure from the spring.

Thanks again.

You need to take out the springs will be running and put in checking springs so you can push the valve till it contacts the piston once you bring the piston to the point where checking is done. You can't check piston to valve if you can't move the valve, checking springs required.

What is an ADJUSTABLE Roller lifter ?

Hughes makes a roller lifter with a screw in/out center. You use a micrometer to measure the lifter you plan on running and then you can adjust the height of the lifter cup to match (with pre-load figured in) and then use that instead of swapping in checking springs.

Since the engine is timed and is running, why would this not accurately simulate how close the valves come to the piston?

I'm using modeling clay, ok...play dough, on top of the piston. I guess I'm not sure why that method can't be used to check PV clearance and the wipe pattern at the same time since it's exactly the set up that will be there when the engine is running.