1 7/8 Header Selection

I'll assume you're talking later Dart ('67 and up) and a smallblock? Any special considerations, like W2 heads?
You could try Jardine Headers (Now Jerry Jardine's Header Palace)- they still have a lot of the old patterns on file.
You could also try ACP Headers, formerly Stahl Headers.
Schumacher has it's Tri-Ys, 1 5/8" into 2" then into a 2 1/2 collector, totally under chassis, fits power steering. Small Block Hi-Flow Tri-Y Under Chassis Headers