I've been wanting to put disc brakes on my 94. But what I thought was that I would need to buy an explorer axle, but it appears that some people are doing just conversion kits. What do I need to do. I've been searching but I feel like I cant get a definitive answer. I know the axle has to be 95 and later, but do sizes change from year to year, that would make a certain year axle better for my application? Thanks.

95 up explorer rear ends will work

if youre looking for one with 373 gears the axle code in the door will be d4
its a 31 spline 8.8 w/ l/s

is there any modifications needed to be done on these axles?

not much you could use the stock spring pearch from the explorer and fab new shock mounts