You need to start with a nominal clearance between bigend bearings, even when allowing for all the tolerances between parts in the assembly.
If the rods should float into each other, the contact pressure should be very low, so just oil should work. Now the question is what material are we talking about. If aluminum, there is still some risk of galling. This risk is significant if the part relationship is designed as "line to line". Steel should be more forgiving, but should still be designed with a nominal clearance.