Dad and I did the engine in a D9G some years back. AJ has given some good advice. The engine will weight around 9000 lbs, with the torque converter attached (the easiest way to pull it). The one on my service truck will do 11,000 lbs, 6 feet out, and I lacked about 6 inches of being able to set it alone. In othr words, you'll need a decent sized crane if you wind up having to pull it.
As far as dropping belly pans, I've done it several times by myself, and I use chains and my crane, but you can use a couple of come-along just as easily, especially if you have help. The way to do it is to hook one end of the chain over the track pad on one side and let the chain drape under the machine. Pick up the live end with a crane, or come-along until it tightens against the pan. Then you can loosen the bolts and lower it to the ground with the chain. it's not quite as easy going back up because bolt holes have to align, etc, but it can be done without a lot of effort.
As far as the oil pan, it should be a two piece unit, if I remember right. Again it's not light, but it can be lowered either with chains or with a jack. Too, having help makes things a lot easier.
As far as the crank, unless it's really screwed up it can be ground under sized without a lot of problem. Your biggest issue is most engine machine shops aren't going to be able to handle the block.
For parts, try Offroad Equipment Parts in Tennessee. They carry NOS OEM parts, as well as aftermarket parts, for CAT equipment. I've ordered stuff from them for maybe a quarter of what the same part would cost from CAT, and in some instances it was a true CAT part, but was an NOS piece they had bought from an auction, etc, etc.
As far as cost, I usually figure a rebuild now days at somewhere around $2000 per cylinder. That includes my labor in and out, my labor to build it, machine shop charges to get the block, head, and crank done, a rebuilt turbo, and a rebuild injection pump. A larger engine like this would add a little bit to that total due to the shear size of the parts, and the difficulty handling everything, but not that much. I would figure on doing all of the above if you decide on a rebuild, as not doing it all is just asking for problems. If you cut off the labor cost, and did it yourself, I see no reason you can't do it for less than $10,000.
As far as a single cylinder repair, that is an option. Unfortunately, you already know, you'll have to tear into it far enough to verify the problem before you do anything else. This alone will be pretty involved. I've got the heads off a D9G right now, and I can tell you for a fact that's no easy task in itself.
Whatever you wind up doing, good luck. If you run into any problems, or need parts, as you can see there are plenty of us on here with the knowledge and resources to find pretty much anything you need to know, or anything you might need parts wise.