There isn't (I think) a ModularGrid system equivalent in 19" rack world.
I am building a new studio in the corner of my home office, based on a unit sized 2x 84hp 19" 21U above a double keyboard shelf, Yamaha SY35 & Arturia Keystep 37 and shelves under with other gear; Blofeld, TR77, RX7 etc.

My question is this.
Will the moderators accept adding full 19" rack synths into the Modular Grid environment? A E-mu Proteus 2500, for example, is essentially a 4U 84hp module

Not sure if it will work with the height but you can try.
Whatever you do please set the Do not list this module flag when uploading.
Mods will delete the "modules" if they appear in the browser.

Thanks. I get all of that. pretty hard to fit the 4U proteus into 3U. I expect a screaming cat in the corner