Yeah that really is your typical Maxell PRAM Battery explosion, Most of the red ones tend to go out with a bang...

The board already is much cleaner than it was, which is good. If you'll get the ROM working, you have quite a bigger change of getting things up and running.

Fingers crossed that the bus isn't damaged under the corrosion

Can you give us a brief description of what the screen looked like other than 'garbled'? any of these?