Depends on what you want to do here. If you are sticking to the stock intake manifold, why not just dig up an exhaust manifold with a working heat riser. If you are set on dual exhaust, Fentons are the one choice but you have to do your homework, they do not fit on every application. Same for Williams. The other alternatives are the cheap so called headers on ebay. Some of these are even made out of stainless steel. Not really a true tube header but does the trick. Finally, Clifford Headers. these are true tube headers, a little pricy but available and useful. I have run Clifford long tube headers for nearly 40 years. Love them really but no longer made.
As for heat, I have run dual carb set ups with no heat and with heat. Heat runs better. I have tried exhaust heat (copper tubes from the fentons to the underside of the intake) and water heat (302 gmc lower therm housing on a 235/261-has water outlet on drivers side of motor in addition to one on the pass side) where you run hot water to the bottom of the intake and then back into the cooling system. Hot water runs better.
As for an exhaust system, from the dual outlets to the mufflers, I have always had to make them up to fit the application. Get around the clutch linkage, and the best way to cross over for a true both side dual set up. I have seen others run them both down one side. Looks pretty cool, but not for me. For tail pipes, cars are easier because you just use dual v8 tail pipes (if the cars came with a v8) or custom depending on what kind of money you want to spend. I have also used two stock tail pipes and cut one up and rewelded it back together to get it to fit on the other side when no dual tail pipe exists. Trucks are similar in that there may not be a pass side tail pipe available so I tinker a bit. I have seen some of the universal dual kits but have not used any myself.
