Not sure how great it would work but awhile back I was thinking about a street sleeper motor. I wondered how having a set of cast iron manifolds abrasive ported would work? It doesn't remove a lot of material so they should still be thick enough to handle the heat and they should flow somewhat better. I was planning on using the 67-69 HP manifolds. I planned on using the same heads and intake you have. You can have the intake done also. The only other thing I can think of would be a set of block hugger headers. Good luck with your project.