I just bought an old Orioin mk1 Diesel box with the 3.58 ratio. I'll take the final drive ratio from that and put it inside my S1 gearbox because I'm sick and tired with the 4.27. My Orion had a 3.84 ratio which was much better than the S1 ratio. It also makes a huge difference to the economy if travelling at high speeds with 5th gear.