For mixture distribution, driveability, and fuel economy, the '78-'81ish 2-piece welded aluminum intakes are the best; they underwent extensive scrutiny at the design phase to eliminate flow dead-zones and optimise the mixture distro to all cylinders, using computerised tools that weren't available prior. There were problems with these intakes at the time; some of them had porous welds that turned into big ol' vacuum leaks. The majority of those were taken out of circulation (recalled/replaced), and most of the rest of them long ago went to the crusher along with most of the rest of the Slant-6 engines. But if you find one in good condition, with no cracks in the floor and no significant warp at the cylinder head mating surfaces (minor warp can be planed flat), that's a good intake to run. The '82ish to '87ish 1-piece aluminum intakes, along with the '76 Feather Duster/Dart Lite 1-piece aluminum intake, are a pretty close second preference.
