...pops,cracks, backfires, lops, wide range misfiring.
Have replaced plugs and wires, dist cap, rotor, modal, coil, pick up coil. No oil in the water, no water in the oil. Compression check 135# to 140# across all cylinders, 10# fuel pump pressure. Keeping engine running as best can, sprayed ether over carburetor, there was no indication leaking manifold gaskets. Tappet covers removed to check okay valve action. Installed new timing gears and chain. Have replaced distributor with one off running engine. Got juice from ignition switch to distributor. Sparks plus replaced three times with new. Have just open fronted timing cover, found NO mistake, gear alignment is as it should be.
What have I missed?

Fernan