I've never worked with two rods, (ha) but unless the 'tight' rod looks as if it is twisting the neck it's probably just stuck with some of the glue used when attaching the fingerboard - a lot of new instruments I set up when I worked had this problem, and you get this terrifying SNAP as the rod breaks the glue - scared the shit out of me the first few times.
After that, just take it slowly. Work in 1/8th turns until you feel how much difference each is making, and trat it like truing a wheel - whatever you do to one side, do to the other, until you are at a suitable equilibrium.
I'd imagine you perhaps want a slight bit more curvature on the bass side, but by working both sides until they are close you can keep things sane and reduce the risk of twisting things, THEN performing the final tweaks.
Take that with a pinch of salt, as I say I've never worked on one, but thats the basic process I would take to get a feel for the instrument.