I removed the pump on my 4020 from the top without taking the front end out from under the tractor when I rebuilt it.  Just remove the fuel tank and related stuff so that you can get to it.  I pumped the fuel out of the tank first and was able to do all of the work by myself without a hoist or jacks, etc.

Later I saw a tractor at the dealer with the front end out from under it and asked what they were doing to it.  Imagine my shock when the mechanic said he was changing out the pump.  I still don't see the advantage of going out the bottom with it.  It is sure safer to leave the tractor on the wheels and lift the pump out by hand from the top.

And it's sure easier to replace it from the top too, rather than raising it from below and underneath before getting it bolted back into place.  Maybe I'm missing something but I am at least experienced with the task and would do it the same way again.  I completed the entire job standing on my two feet in an upright position without anything dripping on my head.  The hardest part I remember was getting the bottom fuel line loose and then reconnected to the fuel tank.  I had the pump out, rebuilt, back in, and the tractor running before the day was over.  It's been a few years now, but I don't think it took more than 4 hours to do the whole job.