Are they the new 5900 batts (taller)?
I'm running the LRP 5900's and they do fit within the cell slots on the FS2 chassis, surely they fit on the FS too, I mean those slots are designed to fit within traditional cell constraints surely?
I found I had to space the posts up too with the taller packs and I also had to drill through the top deck to allow the power wires to input properly.
I think either way you should be OK, upside down or humps facing down.
__________________
|