The one MAIN diffeence in the 440 6-bbl motor was the camshaft had the same duration as the regular HP cam, but had a lower taper on the camshaft lobes for them to better tolerate the heavier valve spring pressure. The cam lobes had a taper on them so the lifter would rotate in their bores and wear more evenly, but the lower taper was deemed necessary due to the heavier springs in the 6bbl motors for greater durability.
From 1968 on, all exhaust valves were the larger 1.75" size, normal or high performance. As I recall, they were first used on the '67 440/375 engines only prior to that (there was a 1.88" exhaust valve cataloged in Mopar Performance/Direct Connection parts that might have first been used on some earlier 1960s "racing type motors". The 4bbl engines did have higher strength valve springs (as was typically the case), with the 6bbl motors being a little stronger still.
According to the dealer's Data Book, the 400 and 440 HO motors also had double-roller timing chain sets. The moly-insert compression rings are listed in there too, but probably pre-date those motors too.
In most of the high performance Chrysler V-8s, "tri-metal" bearings were also listed in the specifications. These were "harder" bearings than the normal spec babbit bearings. Again, greater load capacity for high performance durability, but also less tolerant of grit in the oil. A piece of grit might embed in the normal bearing and be pretty harmless for a long time, but as it would not embed quite so deep (if at all) in the tri-metal bearing, the propensity to score the crankshaft surface was increased. The other advantage is that when you removed the crank for inspection, if the first layer of load bearing area of the tri-metal bearing was worn through, that gave you some idea of the amount of wear that had taken place without having to measure physically measure it.
What the chrome/moly ring is, is a normal chrome compression (top ring) that has an area in the middle of where it contacts the cylinder wall that has an area impregnated with molybdenum for added scuff resistance under high rpm/high load situations. The moly is somewhat porus and keeps oil in it, plus being an excellent lubricator itself. These "chrome/moly" rings have been around for decades, but not used by everyone as they were more expensive. The term "chrome/moly" should not be confused with "chrome-moly" as it relates to hybrid metals used for high-strength roll cages and such--they're two entirely different breeds of cat.
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