Will a 1999 vortec intake bolt to 1996 throttle body injected 350 block?

No, a 1999 Vortec intake manifold will not directly bolt to a 1996 TBI (Throttle Body Injection) 350 block. The bolt patterns and intake manifold port configurations are completely different. The Vortec uses a multi-port fuel injection system, while the 1996 350 is throttle body injected. They're incompatible. You'd need an adapter or a completely different intake manifold designed for the TBI system.