I don’t have much experience in alumni bequests, but many years ago I organised a similar event for VIP gastroenterologist-doctors. What worked well for my company at the time was displaying old scopes
and instruments which the doctors started their careers with.
This groups of individuals are very nostalgic so perhaps going through your archives and finding old transcripts, pictures, thesis examples, books, journals (especially if they are featured in them) and giving them a point of reference they may find interesting. Maybe even some chess boards to assist with the atmosphere. As your institution hasn’t had much contract with them, chances are they haven’t had much contact with each other so may need some prompting. It could be a conversation starter.
Just a thought anyhow.
You could also go the other way and show them how much the school has changed and what you have planned for the future. Past and present. The marketing message or invitation could therefore be more personal, especially if they know they will see their contribution to their particular industry.