You intend to modify an engine for more horsepower that has 100,000 miles on it? That may not be the best approach.
If you have a sound engine, putting on a N* throttle body will increase throttle response but it will require adjustment to MAF table and TPS table. If you use the larger 75 MM TB then the stock MAF will prove restrictive. You will also need to upgrade to a larger MAF sensor like the LS1. The only 3800 engines that you can operate drive by wire are the series III 2004 -2008 engines that have all the components for a synergistic operation. Those engines are hard to modify but you before you get going I would freshen up the long block.
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" 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.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "