Bilge pump installation

Hi, I'm looking at installing a bilge pump/switch in my Cal 28 (original). According to the diagram I have, the keel looks like fibreglass with around 2200lbs (maybe 18-20") of lead below it. Is it safe to drill straight down into the keel 1/2" to screw down the bilge pump and switch? I presume so, but I'd hate it if there was somehow some quirk where the lead joins the fibreglass and a leak started... Has anyone done this sort of thing? Is the lead encased in fiberglass? Thanks for any advice...