On a 3800 swap it is likely that the original fuel pump was replaced but maybe not.
Determine if there is fuel pressure at the schrader valve fitting on the rail as you attempt to start the car. Should be at least 35-43 lbs. No pressure then its the fuel pump, fuel pump relay or an electrical connection. You obviously need a fuel pressure gauge to do this but the threads on the valve are the same as on old R-12 A/C equipment gauges..
If the engine sat for a long time and was not started it is also possible that the fuel injectors are clogged.
" 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, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "