I learned about the Pontiac long rod thing from Dan Whitmore. He used 7.125 rods with .927 pins in 400s and 6.875 rods on 4" stroke builds( I traded those rods from Dan to Tom for a Scat crank)
He told me in the 400s the engine got 200RPM more "pull" out of them. He had a 3900lb TA doing 10.80 with one of his long rod 400s. So it worked for what he was doing. Again, this was with iron heads. Dans health went down not too long after the aluminum heads came out.
Longs rods do hurt your low end. He said you can keep stuffing longer rods in a engine until your 60' suffer if you wanted to.
He also used the sbc 400 as a example of poor rod stroke ratio wearing out the middle of the cylinder bores. He said most of them had severe wear with high mileage. They have the same rod/stroke ratio of a 455 Pontiac so I am sure he put longer rods in those also.
They way he explained to longer rods helping out a 455 was it slowed the piston down at TDC and BDC. Since you could only get so much air though Pontiac heads at the time they ran out of breath early. Pontiac 455s with iron heads and sbc 400 with iron heads ran out of breath about the same RPM. The 455s piston speed is so great it starts pulling away from the "push" of the flame front at a relatively low RPM. Can only get so much air in the hole.
I have proved this drag racing my own 455 with stock length rods and iron heads. It always ETs best when I shift very quickly. See, at first I wanted to rev my engine and went against what Dan said. Then one day I red lit, pissed off and just hit 2nd and 3rd as quick as I could and ran it out. Ran its best ever ET. Dan was right.
From then on I am in 3rd gear before 100 feet. If I am slow on a shift the engine is at a much higher RPM crossing the line, but I am slower.
So, long rods were a crutch and only needed with max effort iron head builds. No one does that anymore.
Just use the rod that fits and concentrate on your engine breathing well.
https://www.youtube.com/watch?v=zn6mwFoI_Ms
So he jammed a longer rod in there to help out a tad.