Another lifter noise question

When I adjusted pre-load with the hydraulic lifters (Rhoads) I put in my 273 engine, I had the intake manifold off. I thought it would be hard to get it right just by feel, without seeing when the inner piston just starts to depress from the snap ring. However, I was fooled the other way, i.e. when it felt like I still had some play in the push rod, it was already slightly depressed. If you can get a thin "USB endoscope camera" (<$20 ebay) down the hole to view, it might help. Also, I think you can fish a lifter out of the bore with a wire (a tool for that) if you remove the pushrod, which I think you can easily do with the adjustable rocker. See if the bottom of the suspect lifter is worn.