Converting spears into halberds

I just got my box and I aim to convert spears into halberds. It irks me a bit to see dwarfs with swords or plain spears, I need something more dwarf like so since an halberd usually has an axe blade part I figured I'd try to do that. Still have to design it on paper but I aim to use plasticard and cut it into the axe blade shapes I want and then add that to the spears. this will be a little bit of a project.

Do any of you have any ideas on how to realize this idea? any bits from other kits you'd use for this purpose?