The 97 uses a DAS X anti theft chip in the key. If the DAS box ( 3 x 5 x 1 inch black box behind the speedo ) does not send the proper signal to the engine computer, the injectors won't operate.

If you do swap engine computers, you must use the matching DAS box and key otherwise the car won't run ( or will just start / stall )

The disconnected fuel pressure vac line has no affect on starting since manifold vacuum is near zero when cranking anyway. The hose reduces fuel pressure when intake manifold is high. This is done to keep a constant pressure drop across the injectors.