You detailed list is very helpful, appreciated and a photo of your keyboard can help me to create a set of mappings.That confirm that the keys are mapped based on the location of the US keyboard, as BACKSPACE is located where the Break key used to be. That is exasperating, I taken a look in to the MAME atari400.cpp original source code and found that [del] key should be used for delete, but it not work on my Mac.