Copper breaks faster..I would use steel 1st then copper .Nylon I would never use on a street machine and like Ricko says put a loop or coil at the ends.
Sounds to Me like too much grease when it gets warm it has to push it out some where Are both sides doing it or just one? Did you put more grease in the other side/ they don't need much.
The old ford 3 speeds with over drive would freewheel when in overdrive But don't remember them not going in to reverse or problems with low gear I wonder if the clutch is cause part of Your problems
Yeah thats helps a lot, What I do is go to local sawmill and get some wooden blocks about 8-10'' x 2' and use that for blocking just make sre You have good level ground or concrete to start with.