The most important thing is to actually lubricate them. Even if you are not using the gears fro thread cutting or auto feed, they probably still turn and wear so keeping them lubricated is important for long life. This includes the hubs. I have seen a great amount of wear on gear hubs that were apparently not properly lubricated by the former owners. The teeth looked great but the center bore had excessive wear. Probably from a lot of idling without lubricating them.
Open gears need something that will stick to the teeth and not just drain off. I have been using way oil but it requires frequent applications. I have seen those demo gears in a clear plastic case at auto supply stores. They demonstrate an oil that sticks to the teeth instead of easily flowing off. That may be worth looking into. I am going to check for my gears. I guess grease would be good for a fixed, enclosed gear chain, but for change gears it could get messy when you store them. Excess oil just wipes off with a rag.
Make it fit.
You can't win and there is a penalty for trying!