i've got a chance to get an apexi n1 for my b18b but its from a gsr. i was wondering if you could somehow cut off the piping and use the muffler and go get the piping redone for the b18b. is this possible? or what are the other alternatives?

 

You just have to shorten the B pipe.

You could do it at home if you have the right cutting tools, and pick up a few exhaust clamps.

 

or a muffler shop will do it cheap