Help Me Identify 727 Trans

I need some help identifying this big block 727. I picked it up as a rebuildable core. I have it apart, and this is what I have discovered:

4 gear front planetary, 3 gear rear planetary
4 clutches in both front and rear drums
small diameter long spring in kickdown servo, no large diameter spring
3.8 ratio kickdown lever
6 springs in front clutch assembly
1970 date on valve body, 3 "month boxes" marked = March, 1970 ? no PTKD.
came with smaller diameter torque converter

Number on case: PK3410 6681 3141 0521

My guess is that it was on an HP 383; possibly RoadRunner or SuperBee.

It was for a 1970 383- 4bbl, from the factory.

Just a plug for Tom Hand's book. He lists all of the serial numbers in an easy to read chart.