Headers vs. manifolds

Dougs And TTI Makes good quality headers that dont leak or hit the ground,fitment are usualy good but you may run into problems considering how bad the tolerances are in the first place on these cars and 40years of abuse are not helping out in that department sometimes there are probably manufacturing isues as well but i think those are rare compared to the isues with these cars.
Another option is Schumacher tri-y headers they dont seem to have got much attention but they sure look like a good product and considering that their bigblock headers has a nice reputation i believe the longer tri-y smallblock version might be a very nice option aswell.

All three will do well at your performance level and will leave you a nice bit of room for future improvements if you end up wanting more power in the future.