There used to be a mopar performance shift kit (P4349469) that made some mods that didn't include any valve body mods. Attached are the original directions included in the kit. This kit included:
1. An aluminum tube (substitute for the accumulator spring)
2. Replacement servo assembly
3. Direction to increase line pressure to maximum
I installed one of these a long time ago with a 383 with 3.55 rear, and it made the used 727 transmission shift early, fast, and pretty hard. Just last week I found the last one I bought buried in a transmission parts box in storage. The box also had a standard rebuilt kit (clutches, bushings, seals), and a pair of new bands.
Plan is to rebuild a mid 70s 727 bb trans, I'm thinking I'm going to use that shift kit in this rebuild.
At minimum I'll order new sprag and clutch springs, mainly because they are so old. Maybe upgrade to the bolt-in sprag from A&A, steel drum, and 5 pinion planetary.... I think you can repurpose the planetary from a 46re - I'll have to recheck the facts that one, my memory is not super clear on that. Might make some sense to grab a 46re from the picknpull, take what I can repurpose and sell the rest.