Your next question is "do I need a split dump pipe" like this http://www.justjap.com/parts/new/exhaust/jjrrbdump.jpg , I did a bit of research on this when it came time for my system, it is proven that a split dump will improve turbo flow, but on the RB25 the flow is pretty good anyway, compared to a WRX etc. My split dump, on the standard turbo, was a restriction above 16psi as it had a 2 1/2" on the big one and not 3" where they merged. The 2871 had a frog mouth front/dump with it so it went in.
Just to be clear on the exhaust order it goes
Turbo- dumppipe- frontpipe- cat
OR aftermarket
Turbo- dump/frontpipe- cat