Which Exhaust Manifold???

I'm finishing (fixing) a 360 conversion into a slant-6 car (74 Duster) and can't seem to decide which exhaust manifold to use on the driver's side. My choices are:

1: Correct high-flow 340/360 A-body with flat pipe flange.
2: B/C/E body 340/360 with 2-1/4 tapered flange (Not sure if this is the correct terminology)
3: A-body 318 with 2-1/8 tapered flange

They all fit with no clearance issues including power steering, but which one will be easier to fit a pipe and get it around steering, starter, etc.? I'm going to take it to a local shop that does a lot of pipe bending for older cars. Will the smaller 318 manifold flow all that much less than either of the 340/360 units?

Thanks!

P.S. Passenger side will remain with the center-dump truck manifold.