This is a common problem, having to do with the way that inst deals
  with version numbering. Essentially, the distributions on the
  Development Foundation and Development Libraries are looking for the
  stock 6.5 version of eoe.sw.base. In order to install successfully
  from these distributions, you must have the following distributions
  open (inst under 6.5 supports having multiple open distributions):
  irix-6.5-foundation-1, and overlay disks for your current os level
  (e.g irix-6.5.6-installation-tools-and-overlays-1-of-2-11-99, and
  irix-6.5.6-overlays-2-of-2-11-99)

  Once these distributions are open, you should issue a keep *, so
  that nothing will be installed from these distributions. You should
  now be able to install the development system with minimal difficulty.