I got a couple of sets of pete gibson's pipes for the B2 model,when i spoke to pete the only difference between them and his S spec pipe was the stinger length being shorter on the B2 to suit the lower rpm peak.
Im almost 100pc sure there gibsons,i wasnt aware Nikons were hydroformed,only Pete and Derek Huxley used to use this method and made pipes for the kr.
Whats the manifold like,an inner and outer section that the header fits between?