I recently swapped headers on my 418 stroker. Went from Doug’s 1 5/8 headers with 3 inch mufflers, to 1 3/4 to 1 7/8 step headers with same mufflers off of them.
The difference was dramatic, and at that point, that was the only change.
Based on the Et slips, difference was roughly 40 horsepower. About 10 more than what several people whose opinions I highly value suspectedI would see.
I was frankly surprised by the difference.
Think you would likely be happy with the swap.
