Here something to think about. My friend that made his version (the first pic) his boring bars go in to a depth of 2", he had his machinist friend make 2 sleeves in 5/8" & 1/2" with a slot cut in them. The inside diameter of the bar that holds the boring bars is 3/4"
The reason is instead of changing the square steel & undoing the nuts & bolts every time you want to change bars he had his machinist friend make 2 sleeves in each of the sizes. When you want to change from a 5/8" to a 1/2" boring bar you just put in the 1/2" SLEEVE & THE BAR JUST SLIDES RIGHT IN. The outside diameter of the sleeves is 3/4" the inside diameter of the sleeves is 5/8" & 1/2" the slot is for the set screws they go through the sleeve to lock against the boring bar this keeps them all one unit. It saves a bunch of time & aggravation instead of changing as you call it carriers you just change sleeves.
Something to think about..