I have had a hedman header on my 78CJ7 with a 258 for about two years now. It does have the dual outlet and it WILL show both top and low end improvements. The flange (important for a good seal) is thicker then that on some other brands I have seen. The price on mine was right around a $130 or so. I would recommend this header to anyone it is a great improvement. I have a custom dual exhaust with glass packs also. If I were you I would go with some good turbo mufflers though. Just my thoughts.
When you switch to headers on the 258 's do you have to change the intake manifold also because they both have to be removed at the same time ,don't they ? what I want to know is can you reuse the old intake manifold with headers ?
Yeah, you can use the same intake manifold with a header. The intake and exhaust are two pieces bolted together. You just seperate the two and bolt them back on. The header comes with a plate to cover the bottom of the intake where the exhaust attached together.