Time to address rebuilt engine oil consumption

4 and 6 are ash fouled.Ash is usually from the oil, but also usually fouls all the plugs, not just 2.
The oily threads tells me the valve cover gaskets are leaking and the oil is accumulating in the plug pockets. The oil then ran down the threads as the plugs were uscrewed.
The compression test may have been prematurely terminated.The engine has to be cranked until the highest pressure is attained.No exceptions.
The results of the leakdown test are not good. Since you say that all the air went into the oilpan, there is something wrong with the rings for sure, or the top of the cylinders have problems, or the tool lies. There is almost nothing as bad as a lying leakdown gauge.A good ring seal will get you numbers in the single digits and all pretty even,and with tight gaps closer to 4% . At least half of those are excessive.
If you unbolt the rockershafts, you can repeat the LD with the pistons at the bottom.That might tell you a little about the bore roundness.You can do a leakdown at any point in the stroke, and find gouges this way, and you can do a moving LD test;you just cant do it with 100psi.With the engine anchored in the frame, you might be able to use 40 or 50 psi though,depending on the length of the bar,your body weight, and physical strength. Its just a matter of re-calibrating the tool. This can help determine the source of the disappearing pressure. If your LD tester has2 gauges, make certain that they both read the same,all across their faces. I hate lying LD gauges.