1 3/4" Headers Verses 1 7/8" on a Healthy 408....Is There a Big Difference??

I'd change them. I'm running the same 1 7/8" Hedmans on my 434 that I ran on my 408. They have 3 1/2" collectors and 3" exhaust to turn downs at the axle. My 408 didn't want for low end, 4.10 gears.