A 2871 is a direct replacement, so nothing is really needed to replace.
When I ordered one, mine came with the 200SX inlet, which replaced with my original GTiR inlet aluminum housing.
I've never had to fit a 3071, but know space is very restricted and its not a straight swap, but someone with more knowledge could answer that better.
When I added my 2871, even at standard boost, I did notice more lag with the turbo (around 4500rpm) as it came on boost compared to the standard unit. I've never had the dam thing over 1.0bar of boost, but when Jim and I mapped it at Oulton Park, the added torque, stripped 4th gear.
I'm keen to see what it will make or deliver at 1.6/1.8bar, but I've got to get the bloody thing back on the road, but those "figures" quoted are, personally, unrealistic and a healthy 380 - 400 seem to be the target area with GTiR's using at 2781.
Thought a GTX2871, sounds like it could offer much more?