4.10 and 235/85 will put you at 2400rpm @ 55mph 4th. OD will turn 1750rpm. You can use a gm nv4500. 92-95 have almost the same ratios as your stock sm420, just has overdrive. The mid 95-pressent has the same case and ratios as the dodge. slightly taller 1st and 2nd. Sounds like you would be better with 4.56 and like a gearvender overdrive. it would let you split your gears and still give you overdrive. 2650 4th, 55mph, and 2100rpm overdrive.
