all right i got a 7.5 " 3.08 conventional diff. i would like to put a traction lok in it instead. can i do it. found one thats not that bad of a price http://www.infernohighperformance.com/catalog/traction-lok_limited-slip_differential_4311382.htm
find a used factory one. they are dirt cheap. get you some used 3.73s from a ranger or ebay and a rebuild kit and you'll be in business. *nod*
there is a site about how to do all of this but i keep losing teh links. =/ yes one can do it... but i don't know your skill level.
its not an easy task.
Shawn's right - replacing a diff is not a task for a hobby mechanic. You need several special tools (dial gauges, etc) and have to get everything together absolutely perfectly or you'll end up with noise and premature wear/failure.
That being said, if you can find one in a junkyard (look in 83-86 Turbo Coupes, 84-86 XR7's, pre-87 Mustang GT's - all of these should have traction-lok) and can score some 3.45 or 3.73 gears it would be worth your while to pay a shop to do it rather than pay for all the aftermarket parts and still end up having to pay to have it installed...