@saad
last time i checked abt 3 months ago, the 4 speed one was for around22k and the 5 speed was for 26k, regarding compatibility of rocky gb with the orignal diffs, it can be done by using adaptor plate, i was also going for the rocky gb on my m38a1, but my orignal gear was in quite a gud condition, so l kept the orignal one.
abt the speed my jeep goes to 100kmph easily (the max speed ive done is 120 on motorway), im running 3c turbo......
Hope this helps
Taimoor