I can personally vouch for the 70's 3-bolt truck manifolds. I too avoided headers for a long time for many of the same reasons. You sacrifice some top-end power, but they are install/forget. I never changed a gasket in nine years. I had to have custom down pipes made (with a H-pipe), but used OEM Monte Carlo SS mufflers and tail pipes. Now, Pypes makes pairs in steel and stainless.
The best ones to find are the pre-smog truck ones with 2-1/2" collectors and have a spreader bar between the inlets. The ones without the bar warp over many heat cycles and you sometimes have a bit of work to get the bolts into the cylinder heads. Some later ones had a separate cast iron flapper valve (make sure you get this or the downpipe won't mate) that backed up flow and forced it through the crossover passage under the carb in stock GM intakes (ever wonder what the quarter-sized metal plates in intake gasket kits were for?). This kind has a flat on the passenger manifold outlet. There are graphite donuts you need to insert into the ends to make a seal with the flares on the down pipes. Just wire the flapper open, or cut it out, then drill, tap and plug the pivot shaft holes.
Generally the studs are toast, but stud kits are in the HELP! section of most parts stores. The tedious part is drilling and retapping the studs when they inevitably break off. If this seems like a lot of work, you will soon forget it as you will never do maintenance on them again. And they do fit the manual linkage Z-bar.
The best ones to find are the pre-smog truck ones with 2-1/2" collectors and have a spreader bar between the inlets. The ones without the bar warp over many heat cycles and you sometimes have a bit of work to get the bolts into the cylinder heads. Some later ones had a separate cast iron flapper valve (make sure you get this or the downpipe won't mate) that backed up flow and forced it through the crossover passage under the carb in stock GM intakes (ever wonder what the quarter-sized metal plates in intake gasket kits were for?). This kind has a flat on the passenger manifold outlet. There are graphite donuts you need to insert into the ends to make a seal with the flares on the down pipes. Just wire the flapper open, or cut it out, then drill, tap and plug the pivot shaft holes.
Generally the studs are toast, but stud kits are in the HELP! section of most parts stores. The tedious part is drilling and retapping the studs when they inevitably break off. If this seems like a lot of work, you will soon forget it as you will never do maintenance on them again. And they do fit the manual linkage Z-bar.
