Took the shaft out just now - pushrods were full of oil, no blueing / wear on the cup at all. The shaft has two identically sized and positioned oil holes top and bottom so doesn't seem like it matters which way it goes.

I'll post up pics tomorrow but there are no witness marks on the pushrods and I find it tricky to tell if there are any in the pushrod holes - the holes have been machined out and it was running 3/8 pushrods and a different brand of roller rockers previously.

Slightly worrying, there was a reddish brown deposit on the valve tips? I'm assuming the roller tips get oil through a hole in the rocker from the needle roller on the shaft?

From the adjusters, it did look like perhaps I could have dialed in more preload on the middle two cylinders where the noise is.

At the moment, I'm thinking clean the pushrod holes and mark them up with engineers blue, then put it back together, set the preload and crank it with the plugs out on the starter. That way I can pull the pushrods again and see where / if there is contact? Should also be able to double check there is good oil flow to the roller tips.