You'd be either getting a 31 spline axle or a 33 spline axle. Most mfg's that offer a T-Lock unit only make them for the 31 count. So you are pretty much relegated to that. There are a couple of 33 spline capable units out there, possibly made by Detroit, but I'm not for sure on that.
The whole posi on the street having to tolerate 500 ft lbs of tq is an oximoron anyway. Street tires will give up their traction way before that, so the stock 31 spline T-lock is adequate IMO if that is to be the intended usage of the car.
8.8's are sturdy enough to withstand that as well, but alot of them have seen too many years w/ either a drag slick, or sticky D.O.T. tire on the ends, and the tubes will actually bend. That is something that you'll need to look at and have corrected.
If you intend to regularly drag race the car, there are other things that will be required to ensure the surviveablity of the combo. A rear end girdle is a must, and there are several out there to choose from. Additionally, you can buy an axle brace kit to keep the axle tubes from bending if they haven't already.On a drag strip, a stock 31 spline T-lock will be inadequate. Again, better to look into the aftermarket like Detroit for something better suited.