Older versions of ABD's releases are at:

/server/gtoal/backup/Elements/home/backup/750m_backup2of2/backup/usr/local/src/imp77/imp-1.01.tar
/server/gtoal/backup/Elements/home/backup/750m_backup2of2/backup/usr/local/src/imp77/imp-1.02.tar
/server/gtoal/backup/Elements/home/backup/750m_backup2of2/backup/usr/local/src/imp77/imp-1.0.tar

/server/gtoal/backup/Elements/home/backup/750m_backup2of2/backup/usr/local/src/imp77/imp-1.0:
compiler  lib  README

/server/gtoal/backup/Elements/home/backup/750m_backup2of2/backup/usr/local/src/imp77/imp-1.01:
compiler  lib  README

/server/gtoal/backup/Elements/home/backup/750m_backup2of2/backup/usr/local/src/imp77/imp-1.02:
compiler  lib  README

gtoal@quattro:/server/gtoal/backup/Elements/home/backup/500gb/backup/gateway-portable/imp77-32
https://history.dcs.ed.ac.uk/archive/languages/imp77-tmp/abd/old/
https://history.dcs.ed.ac.uk/archive/languages/imp77-tmp/abd/