Hmmm seems like something not right, funny that they're all so far out and none of them are tight.
Either the readings are correct or they are not.
Assuming they are not correct - maybe try a different feeler gauge set (or confirm the current ones'thicknesses are accurate with a good calipers or even better a micrometer)?
Assume you have watched videos on feeler gauge technique. With valve clearances like this you can quite easily cram in a gauge that is way too thick (and give yourself fits of panic that the clearances are too big) because the valves are on springs and are somewhat easily pushed away from the heel of the cam lobe to accommodate a misleadingly large feeler gauge.
If you skip to 22:00 in this video you can watch someone doing it on a Rocket engine
Assuming the clearance readings are actually accurate - was it running ok before?
One possibility if the clearances are all large, is that the valves aren't closing right. A compression test might confirm or deny.
Another possibility is perhaps a previous owner or questionable mechanic fitted incorrect shims. Hell maybe they also fitted the cam cover &/or gasket incorrectly too, hence the leak.
If you were to put it back together as is, well you've been riding it as is for a while with no apparent problems.
On the other hand, I'd like to know why the readings are way out before going any further. Lot of possibilities, all we can do is start ruling things out. It's not that much work to remove the cams, change shims and set cam timing. You'll feel much better having got to the bottom of it AND fixed it while learning useful skills.