you mentioned headers so I'm assuming you want more out the eng than just a low perf DD. I'd bite the bullet & get a set of 68-70 340 HP manifolds & they have a ~2&5/16" outlet(s) but they are pricey & might run you $400. The '92/early 93 mag manifolds also have a ~2&5/16" outlets and are a very good choice & will run you $100 + the ride. the later magnum manifolds have a 1&7/8" outlet the same as low po ones & are to be avoided. The very BEST iron mani setup is a 68-70 340 pass manifold and an early mag manifold on the Dr side (it'd be pricey cuz you using half of two different (pricey) sets). The absolute best would be a 68-70 340 HP passenger manifold on BOTH sides. On the DR side the outlet would be pointing forward a bit but its doable or a person MIGHT be able to cut the mani in two & reweld it to position the outlet rearward like the pass one is. As you know ex is the most restricted part of the air pump (the eng) & the 1&7/8 outlets ain't gonna cut it & you know sooner or later your gonna swap in a 360 stroked to 408, so to be proactive...