Langdons(sp?) sells headers and split manifolds, dual carb intakes come up on e-bay every month or two. Edgy sells aluminum heads, and if i ever get my act together I will be too.
use the search function, there's lots of info hetre about hopping up your 6. Flathead six or 6 are good key words. Try www.50plymouth.com and www.inliners.org
I have a suppliers page on my site, www.50plymouth.com , for the parts I used for my engine. Lots of stuff out there for the 230. Pete