Help with extrusion

Hi all,

I’m trying to extend the sides (edges) of this scarab down to the “floor” if you can imagine it resting flat. I’m unsure how to do this with what I have and could use a suggestion - I’m currently working in Meshmixer, I tried solidworks but I couldn’t reduce the poly to repair the part without ruining the model - so I’m back to Meshmixer.

Last year my girlfriend’s father died and we’re making this out of bronze for his headstone - we don’t want people to be able to pry this off by wedging something under it. The model is currently printable and I’ve attached it in case anyone wants a closer look. I hope these pictures will clear up what I’m aiming for: