D4 7U with Frozen chains

The first thing to do would be to take the drain plugs out of the finals to make sure there's no water in 'em. If there is, there's a good possibility the brake bands may have rusted to the brake drums. No water? Back off the band adjusters and brake band support adjusters a few turns to make sure there's clearance between the bands and drums.

if you have a high lift jack, you can set it up and use it to lift up on one of the pad cleats half way up at the sprockets and do this on both tracks. If it moves a bit, a chain to the top of a track and the other end to a sturdy 4wd pickup or tractor should get it moving.

Once it moves, then it's time to try to fire it up but I wouldn't try it unless I knew it was movable. Remember, you've loosened the brakes so they may not work and above all, BE CAREFUL!!

Brakes, main clutch, and both steering clutches feel really free and actually quite close to proper adjustment. All oil levels are good and moderately clean. How would you suggest going about that maneuver with out a high boy jack? Will a tall bottle jack work? Or too much force?

I would try to get the tractor running, if you do get it running the best way is to gently start rocking it back and forth in first and reverse, that will put much more force on the chains than you can do with trying to pull or push the tractor. All around having the motor running, and clutch working will make working on the machine much easier no mater what you have to do to free up the chains.
You don't have to submerge the tracks, although that would be best to run it in water that is deep enough to cover the tracks, say six inches or so, just spraying them down with whatever water you can haul to the cat will help.