intake manifold ports are smaller than what's on the heads

[edmonds007]

Hi, I'm changing my intake from a Performer RPM to another one with Weber 48IDA's and when I removed the Performer manifold and looked at the one with the Webers on it I noticed that the ports on the new manifold are smaller than the ports on my heads. I would like to add that the manifold that I'm putting on the car was previously installed without any serious problems. I would like to know if anyone has any recommendations or suggestions for how I should proceed? As this is my first time really doing anything to the car myself I would welcome any advice about obtaining the best intake manifold gasket. The engine is a Roush stroker 392.

Thanks,
Bryan