open diff. switch to a lim. slip diff.

i got a 93 f150 with a 4.9l 4x4 5spd. i got a axle code 18. which means open diff. and 3.08 gears. i was wondering if it was hard to do a swicht to a limited slip differentail. if i do the switch do i just have to change the gears, or do i have to remove the axles. i want to get the parts from a junk yard and was thinking about getting them swaped out but if it is easier to do it as a weekend job. i know i have to do both front and back. i found a axle code h7 in a f150 that i might go for.