[chiphead]

Is this a roller cam engine with a stock type valley pan? You could have minor contact between the link bars and the valley pan. You'll see witness marks on the underside of the pan. Post pics as soon as you take it off. Don't clean it or anything, maybe a small mark will indicate what's hitting.

Was a stock windage tray used? Sometimes those crack and make noise. That's why most ppl avoid them.

I still like the idea of seeing if the noise is the same speed as a timing light or 2X faster. That would help indicate valvetrain or bottom end.

Dont feel too bad. This is a very difficult and demanding hobby. Everybody on this forum has had a new engine give them fits. It's not easy being a motor head, and this kind of thing earns your stripes.

I built a 235 six for my '54 Bel Air when I was in my late teens. This was pre internet 1990s, and nobody at the local parts store told me that the early 235s used shimstock to set the mains clearance, so I left them out. 150 miles later, I went to change the oil, and the bearings came out of the drain plug looking like curly fries. It was ugly. It wasn't until I got ahold of Langdon Stovebolt and Clifford Performance (Straight six experts, by phone!) that I figured out what happened.