I looked at the thermal 3 inch turbo exhaust at modacar http://www.modacar.com/product...ACAB/
and it only say 94-99 GSR 2dr. But what im wondering is i have a 1998 ls, and think that this wouldnt fit because isnt 94-99 gsr A or B pipe is longer by 4 inch or something???

 

Can't answer your question but you're not going to find many running a turbo 3" exhaust without a turbo (which seems like what you want to do). Normal procedure is to have a downpipe from your turbine exhaust housing and then weld the connector that goes to the thermal. It just comes with a flange that you put on whatever pipe you weld to connect it. Yes you do have to drive to your welder with an open downpipe.

So in short, there is no diff between LS/GSR/etc and there is no A pipe or B pipe.