If there are any working versions of SCUMM Revisited floating around you could probably at least learn the file format using that software. I know Grim's not fully supported by that program, but you could still look at a few things as I recall.
They are in 3do format - there are 2 versions of the format - textual and binary (compiled). The demo uses the textual one, the full game binary. Its the same format used in some of the star wars games (jedi knight?) I cant remember which.
There are a few viewers floating around, but I dont think they support the binary 3do format. If you're still interested I can have a dig around my hard drive, I think I've got a few unfinished Grim model viewers by various people somewhere.