PowerPipe Exhaust for slant/6

Been running Clifford shorties,1 1/2 headers on my race car with the Clifford intake.Am going to try the Aussiespeed intake and want to also try 1 5/8 headers.I cant just bolt a set of any 1 5/8 headers on it because I have modified the car with a rear steer toyota rack.Wondering what the primary length should be for a pure race car,I shift at 6,000 rpm.Have been 11.50 at 115mph and I want more.Would bee very interested in some Hooker headers, cond not important cause I will bee cutting them up to fit my car,dented,rusty,ugly a plus.Guzzi Mark