This engine needs dropping off with someone who knows what they are doing now im afraid. A high pressure leak down test will identify the problem area very quickly.

Testing it with no cams in doesnt really tell you much about the compression as the inlet valves dont open to allow any air in to be compressed, but at least all the low readings were the same which bodes well.

A possibility is the lifters are overpressurised for some reason so they are opening the valves when the cams are tightened down. Maybe wrong lifters installed?
Another worry is the fact it has had new inlet valves. I wonder if the valve sealing was tested when they were installed as ive seen bent / mishapen guides on a YB before after valve impact, and new valves wont fix that problem.

Finally, thinking out loud, there are YB cams out there with 2x woodruff keyways.
Is he CERTAIN the cam timing is correct? Were they set using markers (woodruff key problem wont be fixed) or timed with full lift (Woodruff key problem wont be an issue)