I believe components of the HRS were part of the Blue Steel guidance package whose IN only had to run free for a few minutes. I think that was the basis of the IN package for the Nimrod.
Risking a bit of thread drift here (we can always "on top" a previous post to get back on track!) and harking back to the days of Runway Alignment with the Nimrod's Elliot 103 platform, I believe it was sometimes unfairly maligned. Whilst there was no doubt that it could wander off with the unwary (not as dramatically as an unmonitored HRS) it was also capable of excellent performance. On one occasion; for a special task; we were fitted with a palletised Litton 72, which at the time was "state of the art". On completion of the business we offered the owners of the Litton $50.00 for it, considerably more than its operational value! The Elliot on the other hand performed superbly.
YS