In the air, spin one wheel, if the other side spins you have LSD, While in the air look at rear diff cover it may have a tag on it with gear ratio if not, roll one wheel so valve stem is at 12o'clock, mark the drive shaft and then spin it count how many times the wheels spin vs 1 turn of the shaft.
Easier. I used the ford window sticker, if a different ratio isn't listed it's the 3.31, I checked in the drivers door panel for the axle code. It was GG. Therefore I have a 3.31 LSD.
Which I'm quite happy about. Great acceleration with a 3.31 and the improved economy that comes with it? I'll take it. And I could always upgrade if I decide I need more pep off the line. Though we do not have a local drag strip and we'll probably use this car for family trips in the summer, I'll probably leave it be... Maybe a 3.55 ;-)
Infuriating... Can't, make, up, mind...
Better leave it alone for several months and revisit.