Re: How to move this rock
IMHO, the only way a BX25 is going to move that rock is by rolling it, and even that will be a challenge. You might be able to lift a corner; that's it. Doubt it could pull it, and even trying to pull it with something bigger will likely make the rock dig in. You might be able to make the tractor lift a corner of it (if you're lucky) to get something like a sheet of plywood under it to slide or to roll it, but that's about it. Steel bucket to rock is going to make a mess of the rock unless you figure out a way to use a wood cushion.
Alternative idea: Do you have any connections with someone who owns a wrecker or some other piece of equipment with a big winch? Using fabric lift straps with that setup to pull it where you want would be well worth the cost. Of course this depends on access, pull direction, etc. Depending on your potential anchors, lots can be done with cables, straps, and ****** blocks.