Can I switch intake manifolds?
 

I put a 72 350 in my 94 1500 I'm wondering if I can put the intake manifold from my 94 350 on the 72 and if I cant what do I do to get this truck to run?

No, you cannot switch the intake manifolds. The 1994 350 has a different bolt pattern and is made for fuel injection, while the 1972 350 is made for a carburetor.

To get your truck running, you have two options:

Use a carbureted intake manifold – Get an intake manifold that fits the 1972 350 and use a carburetor. You will also need a fuel pressure regulator to lower the fuel pressure if your truck has an electric fuel pump.
Use a throttle body injection (TBI) intake – Get an aftermarket or modified intake that fits the 1972 heads but works with your 1994 TBI system.
If you go with a carburetor, you may also need a different ignition system, like an HEI distributor. Let me know if you need more details.