Lead is the best and cheapest.

Covering the pan effectively is controlling the source. Gen 2s get 12+dB reduction.
Problem will be now you can hear the air leaks at 70 and can hear your passengers.
Lead is particularly effective w the deep diesel knock.
You will find that as you quiet areas, new sources appear. Steering column transmitts noise.
Tunnel area, rear behind window w some lead is hood bang for the buck. A 1x2 piece in each door.
Foam layer under carpet will help.

You need frequency spectrum to know what works best. If you goo the lead well, it acts as a coupled mass.
M