I'm also 99% sure its level data is stored in SRAM while playing the game, so that's a decent place to poke around in with a debugger.
Good idea. All blocks are dumped around C000-DFFF, as stated here : http://datacrystal.romhacking.net/wiki/Wario_Land:_Super_Mario_Land_3:RAM_map
(that table was written by me some years ago btw
I took a look at moojelly code, and it is really a mess (although some interesting stuff can be found)
I was expecting someone to give a copy of the german document, but maybe it is forever lost.
EDIT : Found something interesting on this topic
. I wish i would have found this before starting hacking WL / SML3.