Thanks for sharing your build with the group. Bummer on the mistake with the 1/4" holes. Just a thought - could you tap them with the thread size that corresponds to the 1/4" hole and then buy some more all thread rods to match that and cut your studs again? Might be easier than the helicoils - I wouldn't know as I have not used them before.
Sorry can't help on the Mac question, hopefully someone else can chime in.