Need some opinions on where to go from here...

I would do a cold again on all of them and then drop oil in them all and keep track of the sealing for them all to have a full test. A leak down is good yes, but it seems we are in the process of eliminating something that isn't as easily located as we hope.

And because you happened to reuse some parts, we are dealing with mix match stuff. You could have leaky valves or valve seals or something in regards to burning oil, my "assumption" is going to be those cylinders letting oil pass through. What did the plugs look like on those cylinders?


The spark plug issue, I have not even thought about. You have a basket of things going on, best to sort out the internal ones first, as to eliminate the need to disassemble the engine and then you can move on to spark related issues sooner. IMO