Hmm…in general I would steer clear of scripting bridge when equivalent functionality is available elsewhere. In this case, you can make use of the Quartz Event Services. There's a Stack Overflow answer here that should be able to get you started: http://stackoverflow.com/questions/1938509/how-to-simulate-a-low-level-keypress-on-os-x

As for the exact problem you're facing, I'm not sure what the answer is. Looking at the AppleScript dictionary, it seems like "command down" and "option down" are special properties in the dictionary, but I don't recall at the moment how to extract dictionary properties from the library. Depending on where you extracted those numeric values from, there's a chance that they could be different on your system (i.e. enums might change between OS versions, since you're supposed to use them as enums and not numeric values).

But the short answer is: your code looks fine, and using enums/numeric constants like that should work as expected in MacRuby. Have you tried the equivalent code in Obj-C to see if this is specific to MacRuby?

Cheers,

Josh