Why not replace the whole axle assembly???

I've been looking at replacing my stock gears and bearings AND then I saw where I should also consider the T-Lock due to miles (134,970 to be exact). Well, all these parts and install kits, not to mention labor, will ONLY cost about $100 less than a new stock rear axle assembly.

UPGRADE:
FMS 3.55 Gear Kit ($250.00)
FMS T-Lock ($240.00)
Complete Gear Install Kit ($110.00)
Still haven't replace axle shafts and other internals

TOTAL REPLACEMENT:
FMS stock axle assembly w/3.55 gears ($799.00)

Mustangs Unlimited has the new axle assembly:

http://www.mustangsunlimited.com/itemdy01.asp?T1=M4006B355+01&Category=Drivetrain&CatKey=74-01

Why shouldn't I do this on a car that will be totally street and probably never see a drag strip or road course??? I have no idea what the installation costs would be, but I'm going to call a few local reputable shops to find out.

Am I missing something here? I'm getting new Cobra brakes (front/rear) at the end of August, so maybe I should do that at the same time. Maybe add in FMS UCA and adjustable rear UCA, also.

I figured someone might have done a total swap. The more I think about it, I believe that I do want to just go ahead and replace the entire axle assembly. The stock rear will be just fine for my future mods, particularly for a street car.

Once I get an installation quote or two, I'll post those.

Thanks.