Rear End Ratio question

My 318 / 904 / Dana 60 with 4.10 ran exactly that. At 70 mph I was running 4000 rpm. The final gearing is 1:1. When I installed the 408 I also installed a 200R4 overdrive transmission. Now I run 80 mph at 2800 rpm thanks to a .67 final gear.

View attachment Gauges.jpg

View attachment no vibration.jpg