351W rockers.

[blykins]

I would check that first thing. With oil additives not being what they used to be, lots of people are struggling with flat tappet cam installs.

I'm trying to think of the easiest way to check without disassembling.

When it's running, are there certain valves that make noise....or do all of them make noise?

If you have a couple of cylinders that seem to be noisier than the others, you could start the engine to build up oil pressure, or prime the oil pump to build pressure. When the lifters are pumped up, you could put a dial indicator on the rocker arm and check gross valve lift.

If you have enough rocker arm clearance/adjustment, you could also adjust an arm so that you bottom the lifter out and make it solid. Then you could check valve lift that way also.

The only other option I can think of is to pull the intake and check lobe lift on the lifter (preferrably solid lifter so that it doesn't compress) or on the cam lobe itself if you have a dial indicator fixture to do that.

I hope this isn't the case, but with it being a flat tappet cam, it's a good possibility....especially when you say that you ran them on the stand but now it's clattering.