Bleeding brakes...

I think if you primed all of your calipers with brake fluid that might get better results.
did you prime the master cyclinder correctly? also check the lenght of pushrod that
goes to master cyclinder.When you modified the disc brakes,you might also have to change the travel of the pushrod.go by the lenght of pushrod that you got disc brakes from. hope this helps. i'll be doing the same thing in the near future. good luck