Cowl to A Pillar filler?

Ok, so I finally have the cowl all buttoned up on the Cuda. I'm sure I could fill the area between the cowl and a pillar using lead without difficulty. Problem is I really don't have any of the tools so I'd have to buy everything needed.

Question: Is there a filler I can use that would be just as good as lead or should I just suck it up and do like the factory?