i just figure it will bolt in outside of the original bridge route, so i don't have to worry about it flying off or something. i didn't know if it would fuck the intonation or something as well.
Couldn't tell you without having measurements. Just take it to a shop and get it filled or fill it yourself. You can't do much with a retarded route like that outside of finding the original trem to put back in it.
I was looking on ebay and found an epiphone with a steinberger trem which I think is the same one that went to your firebird. Not that it's much help but there's some close pictures of it.
the dimensions on my route are 3 1/4 wide and 3" long. can anyone help out with dimensions on the mustang thing? the bridge plate and all.. thanks! im gonna do this if possible.