Need help with 440 break in

I wrestled the passenger side headers out and went to put the original 77 new yorker manifold on and no dice. It's a good inch too thick to fit between the engine and the firewall. I have yet to check the driver side. So what are my options? Is there a smaller set of exhaust manifolds or are they all about the same? I'd hate to buy a set of manifolds just for the twenty minute break in. I'm starting to wish I had broke the engine in out of the vehicle.