transmission Q's and RPO codes

[Bender21]

I have 2 '84 GP's, but my more optioned daily driver is an LG4 305 cid model. Using the RPO codes I have found out a little more about it, but still confused by a couple of the codes. It has the GH2 2.29 ratio rear, but I had assumed it was also a Turbo 350 transmission. The codes I have are MX1 and M31. I have seen the MX1 code, which is a 3 spd transmission, but M31 code comes up as Transmission, 4 Spd, Auto THM 250 Conv Clutch. What does this refer to? How do I check to see what transmission I have for certain? Anything I can check on the transmission pan?
I also have a WS5 code, is this a performance code? I couldn't find anything about it when I looked it up, and the other few WS codes are performance packages, such as Formula package, TransAm package, WS6 package, etc.
I would like to know a little more about it, I plan on changing the gears in the rearend, but I would like to know what transmission I really have as well.
Thanks!

 

[Ribbedroof]

TH250C will have a band adjuster on the pass side of the case, up high, about halfway back.

They may have been marketing the lockup as 4th gear at that time

 

[Blake442]

MX1 : MERCHANDISED, TRANS, AUTO PROVISIONS

M31 : TRANSMISSION, 4 SPD, AUTO THM 250 CONV CLUTCH

That's what is listed according to here: http://www.c2e.info/rpocodes/gmrpocodesGthroughM.html

WS5 wasn't listed.