Greddy DP with 60mm straight back?
 

Since Greddy DP is only 2" and I will be putting on a 60mm Cat back Border 304 this week, will it be feasible for me to fab an 60mm DP to Mid pipe?

That catback is not too much bigger than the stock one. Why not 2.5" (65mm)? That is the general accepted good size for the turbo if I am correct. There is a guy that makes a great dp for the greddy kits. He is turbotony. Great guy to deal with too. I will try to find is email. If you can, open that sucker up as much as possible.

I wish I could return my exahust and get a set of 2.5". The Exhaust shoudl arrive at the door this week, its an 5Zigen Border 304 (Main pipe diameter 60.5Φ ). Let say if i stick with this exhaust system, should I fab the pipe from DP to this exhaust? NO CAT.

It would still be benefitial to upgrade the downpipe as well. Even if it is only 2.38". You'll be happy you did.

I would say if you can, try to get the dp 2.5", it will help if you do upgrade the exhaust later on, plus it will give the turbo a low pressure area right there at the outlet to allow the gasses to enter. As the gasses leave the exhaust, they cool down anyways, the dp is the area that you want to open up the most. Braineak will probably know this a whole lot better, but the science makes sense. Good luck man, hope it turns out ok, I am still rolling around with th 2" dp, and really want to get a 2.5" dp in here soon.