check your hardnose mounts and your engine mounts. is something moving that should'nt be? there isn't alot of clearance for the exhaust pipe of the pony but there should be enough. to prevent touching.
The pony exhaust on my 9U has a curve and comes up right in front of the cross member without hitting it. Maybe you can fabricate one. I Have searched quite a bit and cannot find any pony exhaust pipes or manifolds for the D318 pony.
Make sure the cross brace is installed correctly with the the long side of the mounting flanges facing forward.