4.11 gears-That's what I want to hear.
I have an old '73 Chrysler hardtop with a stock 318 and 2.92:1 rear end. I changed the gears to 3.7:1 and it's like a different car. Unfortunately the old 904 trans has no overdrive so it sings a bit at 120 km/hr- no such problem with the Crossfire.

I reckon DynamicS suggestion to research earlier Merc diffs has lots of merit.

I think the Sprint Booster could be nice but probably not enough kick. I need to get the car faster to, say 120 km/hr, than my wife's 300C Hemi. I think a change in diff gears will do it if I can get the right ones. Right now I can stay with her to about 90 but then the Hemi keeps going.

Obviously an SRT will do it immediately but that's not an option.