What rearends fit these trucks?

[chevymotocross]

My truck (87 2wd swb) has the 10 bolt 3.08 rear. I really want some more pep so I am thinking about going with something like a 3.42 or 3.73. Do all the corporate 10, 12, and 14 axles swap to these trucks? Not sure if the 12 and 14 were offered for a 5 lug 2wd. I should be fine with a 10 bolt, my truck is not built and I don't beat on it.

Lots of used rears locally for sale, just not sure if they are all the same. Will something from say a firebird fit, just by swapping over my brakes and stuff or does it have to be from a 73-87 truck?

Are 3.42 a good improvement over the 3.08 or should I really opt for a 3.73? I have the 700r4 and do a mix of city/highway.