I've trac-locks in both my BII and my Explorer, and I've been disappointed -- especially when compared to the positive "lock" with the G80 "gov-bomb" that my suburban had until it blew up and I replaced it with an ARB. It depends somewhat on what you want the trac-lock to do for you, but I personally prefer a locker to a limited slip.
How are you getting the trac-lock? You can probably get a lunchbox locker installed for less than you can buy a new carrier and pay to set the gears up.
I'm not sure exactly what you can get for your D35 SLA front end, but I believe there are some on here who've put LS's and lockers in theirs. I found a thread from earlier this year of someone selling an Aussie locker for the 2nd gen D35. So you should be able to find something.