With twin truss rods, the process is to act on the treble one first, after freeing the bass one, until the neck is as straight as you want on that side and then slightly tighten the bass side until there's a very tiny slight resistance.
That way the relief will be perfect.
All my Leduc sixers, but one, have twin truss rods, furthermore I owned several Alembics and, I must confess, some Rickenbackers and Rickenfakers too.