Looks like there really was a crazy number of original illustrations on display - looks like basically everything that was in the Illustration Chronicle and, judging from some tweets, some shonen captain covers that have never been compiled anywhere and manuscript pages.
Even though photography wasn't allowed you can see some of these walls in the background of other photos (links because attachments seem to be broken?)
https://x.com/bounce_masa/status/2032836989205258421/photo/3 (this one you can see that some covers were drawn in two pieces - Bio freezer and Sho are isolated and displayed next to the backgrounds for volumes 21 and 22 - which i think i remember takaya talking about in the illustration book for several illustrations)
https://x.com/judy_totoya/status/2033464858277249130
https://x.com/azuma_kazan/status/2033095881805988021
https://x.com/Akito_Nagumo/status/2033036847681778139
I'm fortunate enough to have a friend in Tokyo who was willing to go to the exhibition and pick up the Guyver Unit cushion for me. Very excited to receive and... hug it?