Quite honestly, there is no good choice. Too little clearance, too much trouble with the bolts. Having said that, the Hedman's are as good as any. If it were me though, I'd stick with stock manifolds.
The hedman elites (longtubes) are supposed to be a very good pair and come pretty cheap.
Check out ajusa.com
They give way good deals on hedmans. They don't have the swaps in stock though gotta backorder. Call them up and ask them about part #88668, I got a set of ceramic coated longtubes for $320.00 and free shipping for 1969 Mach1(I needed a headers to fit around a c-6 tranny). Try them out I think youll like them. Cheap, nice, and free shipping. Tell them what application its for they'll hook you up. And if you ever needed to get a beefier tranny you won't have to worry about clearance issues. Hope this helps.