Hi Rick. They are pine car strip weights, available at hobby shops, Michael's and of course Amazon. Lead tape would be good too, perhaps even better.
As to how many, they really fit in there well and I just stacked as many as I could fit.
It always seems like just a little more weight would be perfect but filling that space really did have an affect. I am not really sure why that is since even though the engine is back heavy, it's the rear drivers that have the traction tires, so one might think it's actually better to leave it rear heavy. Idk.
Even if no improvement in pulling power, for me just reducing that bobbing was key. I didn't care for that. It ruined the illusion for me.
My mth Atlantic is a wobbler too. It seems that having just two rows of closely spaced drivers makes it a configuration that easily shows any front-back imbalance.
Good luck!
