I can usually work these things out but I'm stuck and I need other ideas. I have an old junker mtb frame with a shimano cartridge bottom bracket. I went to remove it and the splines from the plastic cup sheared off leaving the rest of the cup inside the bottom bracket shell. Ideas how to get it out? Torch?

Also, the bottom bracket was strange in that it was threaded opposite from normal and the plastic cup is located on the drive side and the bb is inserted on the non-drive side. I've never seen this, so, even if I can get the rest of the plastic out of the shell, I'm not sure I could find a replacement bb. Was this something shimano did on early cartridge bb's? Thanks for any info!