76 KZ400 carb upgrade

So my roommates brother owns a 76 KZ400 and we've landed an opportunity to get his bike here and give it some needed TLC. Apart from addressing some leaks, the plan is to upgrade the carburetors.

I've read briefly here of people doing a single carb conversion, using a Mikuni VM34 and there is another carb upgrade that he's spoken of which is just a "bolt on" upgrade. What I'm trying to do is gather possible upgrades (or... maybe just a rejet?) that have been proposed or are tried and true upgrades.

Any input would be appreciated.