will a stock ITR header bolt right up to a GSR?

 

Yes

 

will it make a difference, is ours higher flow?

 

The primary section is the same, but the secondary is different (USDM is 2 piece), so YES it will flow better. But without the rest of the exhaust - cat that fits, and at least the stock ITR b-pipe and muffler, then the gains will be little or none. ITR B-pipe and muffler are substantially larger and have better flow than the other models, including the GSR.

 

you will need an itr/ls exhaust and cat to make it a "bolt-on"
otherwise it will be too long

 

So it wont bolt on to a GS-R? I'm getting mixed responses. The reason I'm asking is I have DC 4-2-1 that i'm selling to a friend and I want to make sure it fits before I send it to him.