Originally Posted by jimc101

For what your asking about, none of the brands you have mentioned come anywhere near what would normally considered as low end, even the cheapest Rock Shox are expensive vs true low end, Fox are a premium brand, Cane Creek/DVO above that.

Of all the major brands, Fox is probably the best for spares availability.

Would download the parts breakdown PDF's (where available for the fork you are looking to get), and see if what your proposing is possible via same part numbers.

For the specifics
1, probably not, forks are very specifically designed now, the days where you can mix and match are long gone.
2. If not on a manufactuers website, probably not, at least for public consumption
3, Research the parts needed, you will probably find it a lot cheaper to just buy the correct fork in the first place
4, Research the manufacuers specs for the specific fork.

For any 2nd hand fork, would make sure that the stanchions are not damaged/steerer tube is not cut too short, as these are all bonded, the CSU is a big/expensive part to replace if needed