Well guys, thanks for all the information. I bought the six inch exhaust. But, I have hit upon another plan. I know someone with a 3rd Gen Cummins who wants it and he is willing to trade me his stock 4" exhaust for the six inch with some to boot. So, I will probably be installing the 4" system instead of the six. I think I can get enough stuff to fab me a true 4" downpipe and make it fit the 3rd Gen setup. If anyone has done this, is there any quirks I should be aware of from the start? Thanks!

 

Thats a good deal. I didnt realize the 3rd gens were 4". Guess I never really cared to look!
Honestly, in fabbing your downpipe, just make a templet with the old stock pipe to follow, the most crucial part is the FIRST bend in order to clear the firewall. Go to grand rocks web page, they offer a cummins 6bt turbo flange, that will aid big time, or Piers, they offer one as well.

 

airflo also has it. I bought it, a 4" 90* elbow, short piece of 4" tubing, and I had another 90*. About $60-70 in pipe for the entire dp. You could probably make that one work with just the flange and maybe some more pipe inbetween the curves.

 

Thanks rbrettctd. I looked on airflo.com and I believe I can get everything I need there. One quick question though. When I was reading the descriptions of the flanges and elbows they say that some are "3in. inner diameter" while others are "3in. outer diameter." Is the stock exhaust for our 1st gen trucks three inch inner diameter or outer diameter? I also saw that they have what they call a "Flange for a 6BT Cummins." Is that me? Thanks!