Couple of things here. First, the valve covers on my car are in the 7ft. lbs. range. Very similar. You said that you tightened it as tight as you could with a ratchet. 7ft. lbs. would be about as tight as you could do with a nut driver. So a quarter in. ratchet would still be medium tight. Second, don't ever use pliers of any sort on anything that's stripped. Vise grips will work best. In this type of situation, go for the win on the first try, because sometimes there's not a second chance. If the pliers slip, they'll just make the job tougher. Since it all worked out, no harm done, and good job!
Now, on to the flywheel, and keeping things from spinning. A simple trick from back in the day could help here. Try feeding a rope through the spark plug hole. Fill the cylinder up with rope, and leave it in place. Obviously you'll want to leave enough rope hanging out, so it can be removed afterwards. This will GENTLY bind the piston, so it can't cycle. Use a good rope , that won't leave tiny rope bits. And try to coil it into the cylinder as it goes in.
It's been a long journey buddy, and now you're getting close to the end. Don't forget why you came this way, instead of taking the easy way, and just paying the money. The things you've learned here will serve you well, throughout your whole life. Really...its a small price to pay for that kind of education. Keep those pictures coming!