Look at the parting surface of the connecting rod. On one side you'll notice there is a groove extending from the journal bore across the bolt hole (which is also counterbored slightly) to the outside of the rod. The original bearing inserts have a corresponding notch allowing oil pressure from the rod journal to spray out lubricating the cylinder wall, piston pin, camshaft and cooling the underside of the piston crown. Although perhaps not totally necessary, in most cases I would stop short of saying not helpful.
So why did the notch disappear? Most likely when Clevite (being an OEM vendor to Mopar) makes a batch of these bearings, they use the latest revision of the shop drawing and specification supplied by their primary customer (Mopar). Since the Magnum was a roller cam engine, the additional oil spray probably wasn't needed. Also, because it was a catalyst equipped engine, oil control is more important (fuel saving low tension rings would have a harder time controlling the extra oil). And, since the spray hole is no longer in the later rods, why notch the bearing insert. One less machining operation saves $$$.
For high RPM racing engines, builders have plugged the spray hole for years. The reason there is to cut the risk of oil overwhelming the rings and causing detonation (a bad thing at full power/RPM), and windage losses. A 5 HP gain is worth a reduction in overall engine life if you drive 1/4 mile at a time. A street engine which spends most of it's of time between 1500 and 3000 RPM, and is expected to last 50-100,000 miles might benefit from a little extra oil spraying around inside.
As for the full-groove mains, this is probably due to customer demand. For years high performance and heavy duty engine builders have either bought 2 sets of main inserts (and only used the upper halves) or cross drilled the main journals, which costs money. This way the rod bearings see oil pressure for 360 degrees of crank rotation rather than 180. The loss of bearing surface area on the cap was more than offset by the full circumference oil supply which is more than adequate to float the crank, and the bearings probably ran cooler at high RPM. So why didn't the OEM order full groove mains for all engines? One less machining operation, even on half the parts saves $$$.
That's my theory anyhow.
