What kind of intake is this?

X2 on those not being Vortec heads. And that is not a Vortec intake of any kind. GM did call some of the TBI engines Vortecs because they had a ridge in the intake port on the heads to create a swirling effect to better atomize the incoming fuel mixture. What happened was that ridge reduced air flow something terrible. In 96 when they replaced those horrible heads with Vortec heads that ridge was removed, since it was not needed with sequential multi port injection. Because there was no fuel in the incoming airflow until right at the valve where the injectors are located.
As mentioned above true Vortecs have a completely different bolt pattern on the intake manifold and different shaped intake ports on both the manifolds and heads. You can not bolt a 12 bolt intake to a Vortec head. It uses only 4 bolts per head to attach the intake and at a different location and angle. It also does not have the heat riser passage from the heads to right below the carb.

Again the block could be but the heads and intake are not. The heads are what made the 96-00 vortec 350 so sought after. We're just trying to help you understand what you have. You need to pull a valve cover and look at the casting number on the heads. According to Mortec.com that block is used from 95-00. If I was guessing yours will be from 95 before the vortec heads came out in 96.

If you look at this VORTEC engine you will see many things you do not have.
1. Plastic timing cover
2. Vertical intake bolt holes
3. ^^^ on the front of the heads
4. Blocked mechanical fuel pump boss
5. Hydraulic roller cam