Go 1 3/4 unless you are going single plane and high lift cam,and want to rev. For a 450 Hp street motor, in your stated rpm range,I think the 1 3/4 is ideal. That’s what I am going with on my HP 383, street car, dual plane and automatic.
But, with the cost of A body headers I would definitely consider future plans before buying. If you even think you might want more, I would go big now and build up to them.
