Script is up on page 1.
You can have one ROM on your NAND and one ROM on your sdcard as a loop install with your free space provided that you don't use more than 200MB for system and data each with the new script so two ROMs all together, not two loop ROMs on the sdcard.
For example, if you're running KonstaT's JB you can make and install a loop rom on your sdcard. Because of your space limitations you can not do this more than once if you don't cleanup and remove the previous loop files before you make another install. You can use the included cleanup script to remove old or defunct loop-roms.