Okay, so I'm starting to dig into what I have with my car. It's a 1982 320/6, but with a bunch of mods done to that were not told to me when I bought it (a good thing). I cleaned up the tag on the differential and it reads 3.91N3991. It's pretty obvious it's a 3.91 ratio, but not sure if you can tell if it's a limited slip from that. I thought it should have an S somewhere, but didn't see one.
Next up is the front Calipers. Not sure what I have. Rear brakes have been upgraded to disks (323I). Fronts do have vented rotors, not solid. Can't read whats written on the caliper (haven't pulled a wheel yet-maybe tomorrow). They are gold (probably not stock color). Anyone have a pic of a stock 323I caliper or a 320I? If not I will try to post a pic once I have the wheel off unless it's obvious (like says girling on it or something).
Third is my camshaft. Car has an 1984 2.7 M20 Eta motor in it, but idles like it has a cam. Also seems to pull harder than a stock ETA (past 5K easily). Pulled the valve cover today and all I have is part number:
BMW 126447 on one side and LYD4 on the other. Can't seem to cross reference this to any stock BMW cam on the web. This may be a question for the E30 guys, but does anyone know were I could find out what this is?

Thanks in advance.

the calipers look just as regular 320 ones but with a spacer in the middle to accomodate the vented discs. As for the diff, one quick way to know if you have an LSD is jack the car from the diff so both wheels are in the air. Spin on tire and if the other tire spins in the same direction you have an LSD; if it spins the other way you have an open diff.

An "S" is stenciled on the top of the diff under years of grime.

it sounds like someone put the "eta" bottom end in and kept the regular head, and probably put ther 323i front brakes on to as they are vented. sounds like a great buy.

Thanks,
I think it's actually a complete ETA motor. The head has a casting year of 1984 which matches the 2.7 bottom end. I have a few plans down the road. Carb has to go (choke has been removed - makes it very cold blooded). Going to build a mild stoker with either 323I injection the newer 325I L jetronic. Have wiring harnesses for both. Haven't decided if I just want to slap a 323I head (200 or 731) and injection on, or do a complete teardown and build a more agressive stroker with new pistons and an 885 head.
Anyway, will do a little more digging today - pull a front tire and see what's there and also jack up the rear and do a litte differential test..