I started doing IHC back in the 80s. All we had then were damp papertowels in a large glass petri dish and sat the slides on top of applicator sticks broken to fit the dish. The lid was used to form a humidity chamber.
For larger numbers of slides, we used plastic slides trays and boxes, tupperware, etc.
I believe the first automated IHC was by Dr. David Brigati at the Univ. of Oklahoma, who invented the capillary gap Probe-On system. It was marketed by Fisher and used a Histomatic 172 automatic stainer. In 1985, I purchased one to do H&Es. I also saw him demonstrate the first piece of equipment for insitu.
Shandon then developed the Sequenza system that used coverplates on the slides and are placed vertically in a rack with a lid to form the humidity chamber. I still use this system manually! One rack of ten slides can also be placed on the automated Cadenza.
Then came Ventana, etc.