Depending on the specific head casting and rocker arm used, the pushrods may be rubbing the heads themself. I have not run into that issue, but others have.
I watched the pushrods moving up and down, but I didn't see them touching the guides. I'm not sure it would make that sound either, unless they bent, increasing clearance between the valve and rocker. This is not ideal or wanted lol, but what would probably happen is it would wear into the guide until it didn't touch anymore. But this is unlikely since I was observing them.
I had a pushrod eat sideways into a guide a long time ago because the top of the valve chipped and the rocker was canted. I didn't know it was happening until the valve just stopped opening when the rocker arm finally fell off of it. The rubbing was not audible. On the other hand, that engine had a bigger cam and was loud.
I do not think it's in the rocker to valve clearance. Reason being that tick was audible when I backed off the nut on the rocker arm stud. Then I was able to make it go away by adjusting them on the fly. It seems like its just in the lifters. Unless SOMEHOW those danged header gaskets didn't seal. Doubtful though. I tightened those bad boys real good, from the center bolts out. I did a heat cycle on them too, and when I went back to check tightness, I couldn't turn them anymore.
Quite the mystery haha. I'm putting new wheel bearing hubs in there today. After I'm done I'll try and put some mileage on her with the MMO. I will keep you guys posted though.
Gosh I'm really trying to avoid disassembly. My wife will be pissed and I can't blame her lol.