After 35 years back to where i started need exhaust manifold help

Assuming you have the big port 340/360 type heads, get a set of 340/360 A-body stock exhaust manifolds if this is just a street car. The '68-70 340 manifolds have the best flow, but, are also the most expensive to buy. The '71-6 ones work fine too, just a bit worse on flow. Some of the '75-6 castings have provision for the smog ports which you probably won't want unless your heads have the matching ports that need to be covered. The casting numbers in your post # 8 are the ones I would use...either the early matching set, or the later ones.