Ok, sorry for the delay, I had classes to attend.
Attached is a working version of a zealot that shoots Yamato gun (quite funny looking, actually
)
So, the person who said that you had to make modifications to the iscript.bin was indeed right. No changes have to be made to the weapons.dat, and no additional changes besides setting the zealot's weapon to Yamato Gun have to be done to units.dat.
Changes to be made to iscript.bin (I used IceCC for this... decompiled and then recompiled):
Remove the (two) attack1c commands (or comment it out), since that command appears only to work with melee attacks... although I could be wrong for the general case, it is the case here.
Add an attack26 command where the first attack1c command was. (only one is needed, since the Yamato is a single shot attack)
Change the AirAttkInit, AirAttkRpt, and AirAttkToIdle entries to match the ground attack ones. (if you want the zealot to be able to attack air without crashing the game.)
I've attached an mpq with the changed scripts\iscript.bin and arr\units.dat, which can be loaded using MPQDraft. Now
there's a unit with POWER!