Blasting to white and immediately sealing with epoxy
is the way to go, and should do fine. This time of year it'll be a challenge unless you're indoors.
Once sealed, you can use any filling/fairing compound that's epoxy
compatible, but look for something easier to sand and fair. How badly pitted is the keel? How much filler thickness are you likely to need?
Great little starter
boat, btw, it was our first too... (30 years ago next month!!)