Attacking this logically, the likely reason GM went to a 1/8 in larger ring gear was the tooth engagement on the numerically higher ratio (3.73) used in cars with the Th 200 4R. You see, as you go to a numerically higher ratio, the pinion gear becomes smaller in diameter and has less and less engagement with the ring gear. Now, the early SS cars (at least the 83's) that came with the Th 350 used a 3.42 gear ratio which would have had a larger pinion than the 3.73. So, they probably switched when they went to the overdrive transmission, which I believe was in 1985.
1985 Cutlass Supreme Brougham (ex pizza delivery beater with 240,000 miles):
355 Chevy- 9.5:1 compression, Comp XE 262 cam, World S/R Torquer heads with 2.02's, Edelbrock Performer, 800CFM Q jet, Camaro ram air system,Edelbrock headers, Comp Magnum roller tip rockers,TH 200 4R, 3.23 rear, aluminum hood, IROC steering box, poly bushings, Eibach springs, etc. Cutlass build thread here: viewtopic.php?t=4982
Also: The Thing That Won't Die-1998 Nissan Frontier, 340,000 miles of pizza delivery.