I would exercise caution in a DIY turbo project. While you could probably get away with 5-6 lbs of boost an engine must be strong enough and tuned for boost. You just can't bolt a turbo on a used high mileage engine and go. Things like cam profile, variable timing retard under boost, fuel pressure referenced to boost and grades of fuel used, all will have a bearing. There is no way that you will get anywhere near 400HP with the combo that you are intending to swap.
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "