Altough I have a different setup in my 55 2nd series,A 350 cu.in.V/8.I kept the stock 3:90 rear and put in a 700R4 OD tranny.I now have the best of both worlds ,plenty of power off of the line and it cruises at 65 to 75 MPH.Also gets 20 MPG.Same thing should apply to your inline 6.Maybe a T5 OD tranny and your stock gears.