fwiw, I'm just about done putting a new keel on a beat 1980 'glass kayak I'm rebuilding for Karen and the process is a bit more involved because of the edges but very similar in process. fwiw - She always wanted a faster nicer boat than the inexpensive plastic one she's paddled for years. She is small and doesn't have a deep stroke so this will help with directional control and more of her muscle power will propel the boat forward.
Sanded the surface (clean white area) then started by cutting marine grade okoume plywood to shape and used a 2 part epoxy to put it in place. The angle aluminum and paper clips were to keep it standing while the epoxy set.
Gooped up the fillets with Totalboat 2 part filler and used popsicle stick stirrers (Lowes paint department) to get the shape.
Shaped that with a Harbor Freight sander:
https://www.harborfreight.com/power...in-heavy-duty-bandfile-belt-sander-62863.html
Started with a layer of matt along each side of the base then a BID over the top, then BID on each side of the base, and repeated till I had several layers. Below is probably layer #2 for the bases and the ragged edges get sanded off before the next layer over the top. I pinch the glass where it wants to have a void between it and the end of the plywood and you can see the result two photos down.
Here's a trick I use for stuff like this and stanchion bases. Put down your wet glass, cover it with black trash bag, then lay a heavy soaked wet towel over and the towel will make everything smooth and conform to the curves nicely.
Wow - Just remembered in the above photo how rough the surface of the glass was after 40 years of rocks and sand on the Potomac. It's a 13 foot Phoenix that the previous owner wanted $100 for because it had 3 badly repaired holes in the bottom and he figured it was on its' last use. LOL
Pull the towel and plastic off a few hours later and it looks like this:
MUCH less extra resin and much less sanding this way. Those loose fibers in the middle are just the edge of a fabric layer going over the top and sand right off.
Sand it out, fill the rough spots and prime again, fill the pin holes, prime, and sand again, then gloss white withTotalBoat Wet Edge so it now looks like this: