I was going to say what sportmax just said. Seems much more practical to buy an LSD.
I'm not a drifter but I can only imagine an LSD will actually be better and more predictable than a welded diff.
I can get a number of LSDs including quaife and Tomei T-trax
http://www.tomei-p.co.jp/_2003web-catal ... eature.htmI generally recommend the Quaife for most driving conditions due to some big advantages of the helical. I have heard they are quieter. They also have less parts that can wear and don't have the service requirements that many other diffs do.
I have heard many people prefer the T-trax for drifting though.
Personally I would suggest getting good at drifting without an LSD and then seeing if you need one.
Of course my background in getting sideways comes more from rally techniques where you are pushing the absolute limits. In this case it's all a matter of balancing the dynamics of the car to get the rear end out or to keep it out.
If you are trying to drift around a corner at 40 that you could take without drifting at 60 then it will take a lot more work.