I just completed a conversion on my 51,3100, with a 235,I used patricks hurst shifter with the saginaw, I opted to use a ten bolt rear from a blazer,I paid a hundred for the rear and eighty five for the spring mounting kit, used a drive shaft from a camaro had it reworked for 150,00, rear ratio is 3:23,I can now drive at seventy with more to go,You lose a little on the low end. Wth the patricks kit you will only gain 10 mph,and still have the torque tube. I also changed to duel master cylender while I was at it.Good luck..........
