Typically on custom tanks I use a single outlet...in fact I usually just install a barbed fitting...then run fuel line to a valve mounted on a tab somewhere, then to a filter and splitter to feed the carbs.
Like one of these from Dennis Kirk.
i just got the one in the middle for my 160 project off of some online m/c parts wholesaler. Like $16 plus shipping. Probably can find it for less if you look around.
Funny, all the places I looked sold the same selection in the pic above. Some little machine shop in Thailand has cornered the market on cheap aftermarket petcocks.
The middle one's for 1/4" fuel line, rated for engines less than 200cc. Wonder if it'll flow enough? My tank has a metal bung welded in but the frame's in the damn way so I'm going to run a nipple and mount the petcock inline (a la "the Branson Technique"). Easy enough to change out for a larger one I guess...JB, If you're running it inline (rather than screwed to the bottom of the tank) anyway, why not run a filter before the petcock?
Back on topic: 2 petcocks? I dunno. Maybe the tank was designed so you'd have a choice in which side to mount?
Honda go sideways!