Back Brakes won't bleed

Yes, but... Do the other stuff first. Have you determined where the stoppage is at? Flushing that out will help it to not happen again, but it is not going to solve your current problem. If it is stuck you still need to recenter the valve.

What did you meen by 'line is all clear'? did you have flow there?

One other VERY important thing - be really careful turning the line fittings - especially on the block. They tend to strip and when you finally get them to move you may twist the end right off the line.