Yeah, I love those games. I got 20 of them in .. "The Lost Treasures of Infocom" a few years back (or

and it was great.
I installed them ALL in one directory called "INFOCOM" on my original Amiga....
... then, I downloaded a program off of AMINET, called "INFO PREFS" There are actually several utilities on AMINET that will try and help you run those old games from harddrive, but the one I found actually put a prefs program in your PREFS drawer, and assigned all the games to the infocom directory.
From this, you could run one dock icon or button from toolmanager and a neat looking gui pops up allowing you to select which Infocom game you wanted to play.
The fonts, window (or screen), and game are all selectable to your own liking too by the prefs program.
I had mine looking sharp and clear on a seperate screen. Furthermore, the program gives mouse support so you can save each game or do different things.
You should definitely try that for your game. Even if it's for one game, you can change the way it looks and feels with that program and there'll be no problem runnng it.
I got it on my WINUAE (transplanted it over from the 3000) and it runs flawlessly.
As for the ROM image, you should be able to get one off of the emulator's cd. I think....
If you really want to run it off of a floppy image, it's gonna take an .adf file. Which means you will have to get a program called: TRANSADF and fire up the Amiga again and type in a shell: TRANSADF >RAM:Wishbringer.adf -s 0 -e 79
(s = start e = end)
You can also use TRANSROM to suck the rom image out of memory and into RAM.
Oh you might want to adf that disk into smaller pieces so you can fit it onto the 880k. Of course it had better be seen as a "MSDOS" disk in the Amiga by using crossdos or some other PCDISK commodity so you can then transfer that and the rom image to your amiga.
Once you got the ROM image, yer pretty much in business. Do that first.... then do the disk thingy and merge them back together by typing "TRANSDISK COPY"
Hell, the WiNUAE has instructions on this in the help section.. And yeah, it's pretty good for what you want to run.