MN12/FN10 have 28 spline axles and use a cir-clip axle retention mechanism, not a c-clip. As for LSD, when you look on the pumpkin tag, if it came with 3.27's and t-lok, it will say 3z27, not 3L27
It should say something like 88 3z27, means 8.8" 3.27 with t-lok. The tag is up high and hard to see with the pumpkin in the car, they are usually right at the top on the side, mine have been on the pass side generally.
If you don't have a tag and the pumpkin is out of the car, take the cover off and look, you will see an S spring in the differential, I believe this info is all posted in the tech articles as well. Pinion gear will also be stamped with the ratio that is in there, usually there is a part number on one side then on the other it will say 3.55 or 3.73.
I posted the above based on my experiences.
Also, the cast iron pumpkins are stronger then the alum, the cobra guys dump the alums and look for the mn12 irons when they start to make serious power.