The Open University Hektor machines are quite rare and very little information is known. Fortunately found someone with a Hektor III at the vcfed forums, and provided ROMs.
The Hektor 2 and 3 are similar so the user manual from http://www.computinghistory.org.uk/det/43078/Open-University-Hektor-III/
was invaluable, though I don't yet have the ROMs for the 2 I intend to dump them during my next Cambridge visit. The 3 at the museum is actually a 2 in a 3 case.
There are some in-built tests that were very useful for testing:
t - perform system tests
a1 - audio test (plays The Entertainer)
a3 - graphic test
The example emulated also had a couple of extra software ROMs, these are run with ay and az.