I am going 2 to 2 1/8 to 2 1/4 with a 4 inch collector on my 422.
I just sent him his numbers.. it calls for 2.027" to
2.152" dia and a collector dia of 3.686"to 3.936"with
a length of 16.1".... thats for a bigger engine than
yours... if you go bigger on dia it also changes the
pri lengths...remember that is a timed length based on
a dia.... all the specs I quoted are OD with a .062 wall
edit
for a 3 step headers your diameters are close enough but
you need to figure the lengths.. the 4" collector is close
enough also... without running numbers
