An update, ScummVM now has the original GUI (on by default) for every single LucasArts SCUMM game (apart from strange versions like LOOM TG16 since nobody knows anything in the team about PC Engine disassembly...)!
If you want to use the ScummVM menu for saving and loading in those games whose menu only provides one saveslot (looking at you MANIAC v1...), just use the good old CTRL-F5 combination.
Also, this!