I need some help on things to look for. We built a 355 SBC for my brother and it has a vibration at the back of the RH valve cover. It's a basic 350 with flat top hypereutectic pistons, CC XE268H cam, vortec heads. If you move forward on the cover the vibration goes away or if you feel on the other cover the vibration isn't there. It has vortec heads with aluminum center bolt valve covers so we thought maybe one of the rockers/springs was rubbing against the valve cover. We removed the cover and couldn't see any signs where it was rubbing. We then thought maybe it had a bent push rod since the heads have screw in studs with guides. We removed the back three pushrods and rolled them on a glass and didn't see anything wrong. We can't hear any knocking or any sound with it (it's a little hard since it has open headers). Any suggestions on where to look? TIA

It still could be rocker arm contact..I had that problem with mine and though I could not distinctly tell where the contact area was that in fact was the issue. Might not be your problem but you might try doubling the vcover gasket or one of the thick ones that are out there. Might also look closely around the baffle if the valve cover has one.

You can try moving a couple rockers and pushrods from back to front. If the motor is fresh, I can't imagine it would do any harm to run for a minute like that. You can always put them right back. if the vibration moves or disappears, you're closing in on it.