What's wrong with my motor?

I have a 74 Duster with a 360 and since last fall when I got it running again, it has been making a huge rattling noise on the passenger side of the motor. It sounds more like a deseil tractor motor than a gas motor. I've replaced the lifters thinking it was lifter noise (which my brother agreed with after listening to it), and just recently I dropped the oil pan to check the windage tray, which was all fine. So far nothing has changed the noise.

The motor sat for a couple of years when my buddy owned it, but while it didn't have gaskets, it was buttoned up with heads, intakes and sheetmetal. I put it back together before dropping it in the car with the heads he had been running on the other motor he had in the car. The cam is the same one I put in the motor back in 92, but it all looked visually ok and probably only has 50,000 miles on it.

What I can tell is that it does not look like it is getting oil to the rockers. When I look down in the oil fill holes, the rocker is not filling with oil. So, it seems to me that the noise I am hearing is the lifters not pumping up because they aren't seeing any oil pressure.

When looking at how the oil passages run , it doesn't appear that the lifters on that side of the motor could be starved without the rest of the motor not seeing any pressure. Does that make sense? The oil pressure seems fine and the left side of the motor is quiet.

Would the rockers make a bunch of noise if they weren't getting oil, if the lifters are pumping up? I could see the passage being blocked to the rockers with a bad headgasket, but I'm not sure it would make the noise it is.

Any ideas?

This is the numbers matching block, so I'd rather not screw it up. Really don't want to pull it, but I'm running out of ideas.

Thanks.