If all I needed to handle a situation in an emergency was a ms180, I would just get an axe or a hand saw or it could probably wait until the emergency is over. A couple batteries on an ego is probably a better option.
That looks pretty good. Those chips are normal for cast iron. You could easily cut the ends of the new jaws flush with a hack saw or cut off wheel. Then file or grind smooth. Whats next, full paint job?
I'd expect to see some shiny metal on those area if some thing just happened to that ratchet. That looks like the design of that ratchet would let in debris to wear it out pretty quick. Aside from the entire mechanism cracking in half immediately after buying I wouldn't expect a free 40 dollar...
You'll need a chain spinner tool to put in new link. There is no master link on saw chain. You have to buy preset links to make new connections. It might be worth it to ask if a local shop can add the links or you.
Looks like water has been getting in. You might consider 5/4 deck boards so it can drain an breathe a little. And get the entire floor structure up of the ground some.
I've heard them called railroad jacks. They will lift a lot. I've used them with a wood handle about 2-3 ft long. Great for lifting buildings/sheds/camps with sill beams. You'll probably have to make a handle