Intake Manifold Questions

I am beginning a propane conversion on my '75 258. I had previously installed an offenhauser intake with a four barrel carb, bad idea at altitude. I had to file down the bottom of the offenhauser intake, where the stock exhaust manifold would attach to get it to fit over my header.

Now that I am going propane, I need to put a 1 or 2 barrel intake manifold back on the motor. I still have my original 1 barrel intake, but it is open where it once connected to the exhaust manifold and won't fit over the middle two outlets of my header. How can I plug the hole on the bottom of the stock intake and modify it so it fits over my header pipes?

Is there a newer 2 bbl intake (ideally aluminum) that is independent from the exaust manifold with the same bolt pattern as my 1975 block?

Could I pull an intake from a junked 1980's AMC and get it to work?

Any help is greatly appreciated!!

 

The 258 intake manifold after 1980 (81 on) is a 2V and aluminum. It uses a steel pipe, sort of a large diameter piece of steel brake line with flare nuts on both ends, to pass the EGR gas from the exhaust manifold to the intake. The 4-bolt intake heater powered by exhaust gas is gone, replaced by an electric heater.

I can't guarantee that the aluminum intake manifold will clear your header, but the early and late manifolds both bolt on to all 232 and 258 cylinder heads. I'm using a set of 1985 CJ manifolds on my '77 truck.

 

Thanks for the advice, Is the manifold heater essential for me to hook up, or could I just plug the holes?

 

There's a hole for the exhaust gas, but it's for EGR. You could use it or not, depending on whether you want or need smog stuff.

There's an electric heater under the carburetor that helps to keep the fuel vaporized at startup. I'd expect fuel condensation would not be a problem with propane, so you probably don't need it. If you remove the electric heater, you'll have a 6" diam hole to fill on the bottom of the manifold - I'd say leave it in place and unplugged.

 

I don't need any smog stuff, I'll just leave the electric heater like you said. Thanks alot.

 

What are the torque specs for the intake and exhaust bolts?