There is a "lazy" advantage to using large carburetors - it's easier to pin down which circuit is in play, since each covers a wider range of engine speed. With 2 × 28, you're using the float level, pilot jet, idle mixture adjustment, slide cutaway and needle jet size and needle taper & position at 50 mph. With a larger carb the needle is "invisible", which may help or shorten diagnostics.
Easiest: if you have carbs now, what jets are in them?
If you buy a commercial kit from a known source they're generally close enough to run out of the box, how close you get depends on your patience.
Biggest mistake: buying generic carbs, then $pending on tuning parts - very costly.