So, with that roadblock hurdled (Saturday of labor day weekend), it was on to my light shelf. A (literal) cross section of my light shelf looks like this:
The shelf has a 3/4" pine lip sticking out, with a routed edge that sort of made it look like part of the crown molding, with crown molding underneath. The old crown molding was only 3", my current ornate crown is more like 4.5", so my new lip would stick out a bit more. I had kept the old lip pieces, but I'd need more as my ceiling rework gave me significantly more light shelf than I started with.
I picked up a few pieces of 12', 9" wide 3/4" pine at Lowes. A good router bit set I picked up a few years back had a bit that matched the profile of the lip edge. I used a mix of the old lip and the new pine, but even when I used the old wood I flipped it over so that I could route a new edge. That way all the routing would be exactly the same.
One minor issue: since the old shelf wood was only ~7" wide, it didn't make it all the way to the back of the shelf. Not a real problem, but it messed up my attachment plans. I was going to drill at an angle up through the front of the light shelf and screw through the 2x4" up into the shelf. Unfortunately, the short shelf made that hard. I was too cheap to buy more pine, so I improvised.
I ripped some spare 2x8's at a 45 degree angle and screwed them into the front of the light shelf. The would act as something to nail the crown molding into, and I could also drill/screw up through them into the shelf:
That worked well on a trial piece. So, I got out the miter saw and started cutting my light shelf pieces. These are all test fits:
I painted the front of all of them gold:
and screwed them into place. I was quite pleased with all my joints in the end, but there were some frustrations during the final install. Specifically, as I was working my way around the room little errors started to add up, until I got to the back corner over the door and it was just too far off for my happiness. I ended up unscrewing and reinstalling about 1/3 of the room.
My lesson for next time: install a few big pieces first (in different parts of the room) as sort of anchors (with at least two pieces between the anchors), and then fill in between the anchors. That way there is less room for the error to build up.
Now, on to crown molding...