New fir headers are expensive and the wood just doesn't look right, so we like to rescue the old trim whenever there's the faintest of heartbeats. In this case, the notching (I guess if you consider mauling the top of the trim randomly with a gouge 'notching') along the top edge we could ignore - no one will ever see it unless they're up on a ladder. We're cool with that.
The notching on the ends of each header need to be dealt with - you'll see it for sure, though it will only really be visible a teeny bit on the end grain and peeking out from abutting the vertical moulding. So, Ken cleaned up the end notches by rabbeting them to a nice, square cutout. Then we resawed a piece of fir we had left over from a previous plinth block project. And now, they're gluing in the basement - soon we sand them flush and stain the whole schmear. They won't be perfect but they'll be good enough - you'll only see little parts of this around the other trim. (note: this is the back you're seeing in the photo - the front is perfectly fine-looking).
That's about all we did this weekend - the sun was out and the garden was calling. We finally managed to clear out all the leaves from the yard before they come by with the city's leaf sweeper-vac machine - ha!