slagburn

Hi, kind of a dumb question but sometimes you gotta ask. I have a 410 ci engine I rev to 6500, looking for at least 550 flywheel hp. The headers are big enough but I don't know about the rest of the exhaust. It's dual 2.5, mandrel bent back to two Magnaflow round mufflers. Would I see that much difference going to dual 3 inch? The motor doesn't top end like it should and I think the exhaust is plugging it up.

thanks.