Yeah, The Flex-Pipe Doesn't Work...

Just make some templates out of cardboard to show the shape of the pipe you need and have a local exhaust shop bend them up and weld on the proper flanges to mate to your manifolds. Ideally you want the ID of the pipe to match the ID of the manifold outlet for at least 12-18" back to keep the velocity and scavenging up. Yes there is still some scavenging with manifolds just a lot less than headers and it's more sensitive to the pipe coming off the manifold.