Can I get away with stock 318 exhaust manifolds on Magnum crate engine?

I just struck a deal with another FABO member for a nice lightly used Magnum 300 crate engine that will replace my old 318.

Until I can wrangle up some more cash, I am hoping to run my stock 318 manifolds.

What do you think? will I be able o get away with these for a while? Will they really strangle the engine?

Thanks for any opinions!