Sirius is correct, keeping the originals and reference material is an important part of the provenance and history. I actually have that issue (no missing return slip though!) and the IES machine is in my SCMP notes with its use of 5 bubble displays - one per register...
They also mention a range of expansion cards in either LCDS ro ETI 31 way connectors...
Also on page 36 is the source of the Mullard Amp modules I based my home made stereo on
https://twitter.com/timbucus/status/1258778407489413122