It's probably the VATS or Vehicle Anti- Theft System. You or someone with the ability needs to unlock it. I did a swap into my 92 and had the same problem but once I unlocked it with HP tuners it fired right up.
SOLD:1992 ECSB Silverado lm7 5.3 Swap, TR220 cam, Circle D 3200stall, CBM street tune, Schoenfeld LT's, LS1 efans, transgo hd-2 60e, custom CAI, Autometer gauges
Best 1/8 E.T. 8.86 @ 77.8 on 275/60/15 MT ET Streets with 1.92 60 ft.
2000 RCSB 4x4 Lq9 swap...stock except mild 4l65e....for now