The Driveshaft Shop sells them, and level 5's would be overkill on a 400 rwhp car. Level 2's are good to 600 rwhp. DSS shafts are awesome, but they aren't cheap at all. Level 5's go for around $2k. Amazon is doing a group buy, so you could save some money. Details can be found here: http://www.svtperformance.com/forums/showthread.php?t=155753
Edit: These won't work on your 99 unless you upgrade the carrier to 31 spline. 99's are 28 spline. Raxle makes some good halfshafts for the 99's. I think they are under $600 for both.