Headers

What size headers would you recommend for my engine? 414, m1 intake, .590 cam, speedmaster heads (non cnc and untouched for now) 12-1 comp. I have no idea how much power it actually makes. 1 3/4? 1 7/8? Was looking at hedmans because I like the slip tube style and non welded collector flange.

Car is a 73 duster