I've got a 3.9 front a and rear diff sat here that im now not using in my race car I have already sold the drop gears the rear diff is a std ford lsd.
I didn't fit them as I bought a quaife SCCR dogbox and need to use a std ration diff or it wouldn't hit 140
I'm told the 3.9 front diff is weak due to the number of teeth on it but it could be just a myth might be worth a try..

steve