I found a bad spot on the Baja where the k-plane was bolted through. I managed to get it all cut out back to good wood and now need some help scarfing it back in.

I have cleaned everything out back down to the glass What is the best course of action to make this repair. Between the wood and glass and on the sides and bottom was an epoxy type material that was very hard. What is this product? Is it a "filler". Any help would be appreciated...

The 'filler' was just whatever they used to bed the wood into the transom. When I did mine it looked like resin mixed with talc, looks the same as yours.

You can use resin mixed with cabosil, aerosil, high-density filler, any of them will work. Spread it on with a notched trowel and press your new plywood in.

I would suggest more overlap between the plywood layers tho, at least around the top and upper stbd side of your cutout. You don't want to get too much closer to the transom ring, you're going to be pretty close when you lay your new glass as it is and you have to keep that mounting surface very straight between the inside and outside of the boat, as well as across the inside and outside.