Well, it turns out the synonyms block is no longer supported from SCI01 on. LSL2 and SQ3 didn't use it much, if at all, so it doesn't affect them. KQ4 and LSL3, on the other hand, use it quite often, so I'll have to adjust the said specs to not use it.
By the way, I've managed to test LSL3 to completion using the S.old.010 interpreter. Next step is to port to version 1.000.172. As with SQ3, there is actually a German Amiga version of LSL3 that uses SCI1, and has SCI1 sound resources... but they have no Adlib tracks. Nothing Sounder can't fix.
The only things that don't work are rm140's RoomScript (the age quiz) and rm340's ComicScript (the Comedy Hut's inputting of ethnic groups). For the former, I just couldn't decompile it ("Couldn't find DUP source: 20"). For the latter, I had to do some tricks to generate workable code, but it doesn't work right (fortunately, the sequence is still completable, so you still can get the full 4000 points)