Header options for a B-engine stroker in a Dart?

See what TTi has to offer but some fenderwell 1 7/8 or maybe 2" would be the best bet for power.You can do the tri y just expect to be down on power.
If you redid the collector larger and ran a 3" exhaust it may minimize the losses a bit but you need at least 1 7/8 tubes.

2" would better for lower gears/higher stall and more racing oriented but 1 7'8 will be make a nice street power/torque curve.