Agree with Wayne, sounds like your piston rings have seen better days.
As for a litre every 600 miles, I top mine up every 6-8 weeks, usually less than a litre, and the car will have done 2.5k-3k miles or so in that time, on a (now) 185k engine.
Take anything off of it worth flogging, and send it over the bridge imo.
I understand, however, if you are massively attached to it, but be prepared to spend a fair bit of money getting it up to scratch. Ask yourself is the car honestly worth it? And are there more bills on the horizon? Aside from the welding, you are probably going to be best off dropping a second hand lump in rather than getting the engine you have stripped to have the rings replaced (and who knows if there is anything else...). And then you can never tell if a second hand lump is going to be much cop.