How much would be left on the table?

i run TTI LA 1-7/8'' headers on my w2 436''. not ideal but all i had at the time and the money tree dried up!

made 653 hp and 590 tq.

maybe 5 hp is lost due to the headers.
So on your 436 inch W2 motor, your saying you would only lose 5 HP going to a 1 5/8 header?