There is no ridge to speak of, just a small ring of carbon which can be scraped away with a knife. Otherwise the bores are score free, but I'm frightened to force the pistons and score the bores. It's a three cylinder motor and I believe # 1 cylinder is the one sticking.
Half blocks are not available and a new motor is $3800, which I just can't afford at the moment.
Well if the pistons are seized in the bores it is most likely to be the rings that are rusted to the bores. I have seen ali piston corrosion but that was in long abandoned engines.
Mix 80% diesel and some transmission fluid or any thin oil and let it sit in the bores for a day or two.
It is best to strip the engine removing the crankshaft but providing the pistons are not at BDC or TDC I have freed off engines without doing this.
Make a round hardwood plug the same dia as the piston and about 6 in long.
Now get a big sledge hammer at least 10 lbs and give it a real whack. Protect the block with some wood if you are not good with a hammer.
Most times the piston will move. You may break the rings though. A ring replacement is cheaper than a new engine!
When I was running a garage we would go out and get all sorts of abandoned / negelected machinery and get them running again. We were not always successful but I think our strike rate was about 90%. Many of these had not been run for 10 -20 years.