i run a fiesta xr2i 1600 cvh in the boss and the welsh saloons i took apart a rs 1800 zetec fiesta box used the gear set onto the xr2i cvh shaft so close ratio then fitted the 4.06 crown wheel to match the shaft chucked in a quaife atb diff then fitted the 5th gear off the cvh xr2i gives alot top end oh and done all the bearings and seals any one intrested i can give you the gear ratios if you want on paper at 6000rmp should top out at 134 mph but 1st 2nd 3rd and 4th are close ratio from the rs1800 zetec been in all season and no problems ues a good oil top tip