"Therefore, what will I have to do to modify these carbs to fit my ped."
You'll have to do what you have to do.. that could range from nothing at all to drilling oversized mounting holes to custom-casting an aluminum adapter..
"I’m "assuming" that the difference in the carb sizes comes from the intake size."
Carbs are of a particular size for many reasons, mostly related to reliable performance under the conditions for which the manufacturer of the bike thinks the bike will be ridden.
The "size" of a carb (in millimeters) that you mention is that of the venturi near the main fuel jet.. This is the smallest diameter of the carb's throat and has nothing to do with any intake (whatever you meant by "intake").
" Therefore, if I bolt a 15mm carb on my bike that uses a 14mm will I have to step down the metting jet and/or adjust the float level?"
You may as well ask "If i go fishing, will i catch a fish?" Despite all the books and knowledge and advice available, nobody in this world knows what will happen. Your bike/engine is unique. You are modifying it in a way that nobody can predict the results.. Generally speaking, i could give you some useless theoretical advice about carb size and jet size and float levels but that's just a waste of time.
Find a carb closest to stock. Do what you have to do to bolt it on. Read and learn. Buy some new spark plugs and do 'plug chops' to determine rich/lean mixtures at different RPMs . Study. Examine things.. Study some more.. Test ride the bike. Do some more reading. Determine whether it runs the way you want it to or not. Learn how you can modify it's behavior if you choose to. ...........
BTW, any given carb has only one proper float level.