Transmission decoding help, please?

[nikwho]

Hello all,
Just picked up a TH-400 transmission from a buddy. Was in a square body C20. Here's the info that I've pulled off of it so far:

Off of the pan rail:
C73170243

Off of the tag on passenger side:
420
77-CP-40087

Thanks for any help that anyone can offer!

[nikwho]

The 420 stumped me, but I believe that it is to represent the 420th day of 1977, or the 55th day of 1978.

From my reading, the CP would indicate that it seemingly came from a 1978 454 V8 Series 10, 20. It has the short tail housing, so unfortunately I will have to have a new drive shaft built, being that my '68 SWB GMC currently has a TH-350, with a slip yoke. I am hopeful to find a LWB driveline with an integrated slip fitting built into the shaft. I'm thinking that if I can find one and have it shortened and balanced, I should be money ahead. I'm cordinating my TH-400 swap with my 12 bolt axle swap, so that I should totally swap over from 1310 u-joints to the heavier duty 1350 u-joints.

Is there any other relevant information that can be had from the codes that I found? I guess that'd be about all that I could think of that I'd need, as far as the tranmission goes.