im having hard time getting the right parts for my del sol

i bought the tri-t replica header on ebay but im not sure if it was for gsr or b16
and there was maybe about 6-7 inches of space between the header and catback pipe.
not enough to fit a cat so i had to weld a flex pipe.

now i want to buy a different header but not sure if i need to get a gsr or b16 header.

how much difference in length are we talking about between gsr and b16 downpipe