The syntax is the same, yes. But Saids and synonyms are not supported in SCI1.1. synonyms just won't be output in the script resource, and I'm not sure what happens if you call Said. I would guess it just returns false or crashes the interpreter.
Since, other than a few fan games I've seen, everything is text-parser based, I can't see this as being much use.
At any rate, one other reason it might not work is that the interpreter makes assumptions about some of the classes. In particular the offsets of certain selectors need to be at certain positions in the classes's property list. We had issues with this before when moving the SQ5 decompiler source to the LSL6 interpreter.
Probably the easiest thing to do is to create a new SCI1.1 game, and copy your source files in there... but not the ones that overwrite Actor/Prop and such. Leave all the SCI1.1 base classes there. Just copy over your room classes. Hmm... well, now I'm not sure. I guess you still want all the menubar stuff (which is not used in the SCI1.1 template game, but I think still supported by the interp). I dunno, hurts my head to think about it. I guess... give it a try? The issue with selector positions I mentioned above is just a problem with Sierra's interpreter, not with ScummVM. So if you manage to get it working in ScummVM, there's probably some tweaks we could make to have it behave ok in Sierra's interp too.
I don't think there could ever be a tool to do this automatically though...
