Well I'll answer my own question in case anyone is searching.
This "solution" is besides sending the keel to an actual foundry.
The guy at Hunter suggested putting in lag screws, which is not ideal,
but pressed for time, that's what I did. I drilled into the led with
a 3/8" bit, and put 1/2" stainless steel 3" lag screws. Note of
caution - use plenty of wd-40 or some lubricant or the bolts can get
hot and bend. Hand tightening the screws from the beginning is the
way to go.
A more ideal solution, which I'll do later, is to drill into the side
of the keel to meet a 1/2" hole straight down, and put in 1/2"
stainless steel or brass bolts. Put the nut in from the hole in the
side and fill the hole.