Today while working on my 90 Blazer I noticed that the passenger exhaust manifold was cracked back towards the firewall. So, what should I do? Replace it with an OEM manifold or get a set of shorty headers? (I live in the Peoples Republic of California so I need to stick with smog legal headers) I have a hi-flow cat and a cat back flow maser exhaust already. Would headers really help me on power and MPG or should I stay stock. Thanks Dan..