OK, sorry for the delay. Here is my first draft of a response to this very reasonable question. It had to be pieced together from a number of places.
The main identification is on the bottom of the transmission, in the middle, on a raised surface, which is sometimes scraped from bottoming out on the pavement.
G50 04 3K 00542
This would be a G50/04
3 = index of "variants", example, 1L is plain 1990, 2L is M220 (LSD) 1990
K is the model year. K= 1989, L=1990, M=1991, etc.
00542 is the serial number, typically starts at 501, or 2001, or whatever.
The number on the side housing like 950.301 is just the casting part number for the housing -- tells us nothing really.
**The numbering was much shorter and less informative prior to 1988. So if you have an early G50 from 1987, or any 930 (early turbo), the numbers do not follow this outline. Otherwise, here we go.
G50.00 1987-1989** 3.2 Carrera, Rest of World version
G50.01 1987-1989** 3.2 Carrera, US/CDN/Aus/Jpn version
G50.02 1987-1989** 3.2 Carrera, Swiss version
G50.03 964 C2 1990-1992 1L is plain, 2L is M220
G50.04 964 C2 1990-1994 Swiss version
G50.05 964 C2 1992-1994 US/CDN version including RS America
G50.10 964 RS (street legal basic race car, non-US)
G50.20 993 C2 US/CDN/Swiss version
G50.21 993 C2 ROW
G50.31 993 C2 RS version ROW only
G50.32 993 C2 RS M003 (clubsport) version ROW only
G50.33 993 C2 RS Swiss version only
G50.50 3.3 Turbo 1989 first G50 turbo version (larger ring & pinion)
G50.52 965 C2 Turbo 1991-1994
Turbo = rear wheel drive
Twin Turbo = all wheel drive except for rare GT2 ROW race version
Carrera = rear wheel drive
C2 = Carrera 2 = rear wheel drive
C4 = Carrera 4 = all wheel drive
I will skip over most of the G64 (allwheel drive) versions, and all of the A50 (automatic, also known as Tiptronic) versions, and all of the Z64 front-drive transfer cases.
Some of the G64's can be converted to two wheel drive. That is another discussion.
Briefly:
G64.00 and G64.01 964 C4, not readily converted at all
G64.20 and G64.21 993 C4 trans, readily converted to 2wd
G64.51 993 twin turbo all-wheel drive trans, readily converted to 2wd
When the index of variants says there is M220 Limited Slip Diff, it only means that was what was in there in 1989 or when made, there could be something else in there now, or more commonly, a worn out limited slip diff that acts like an open diff. Also another discussion.
Now, what is/was the confusion? Whatever it is, it is probably understandable, Porsche did not make this simple, nor widely known.
My apologies in advance for any typos, errors or omissions.