I spent some time drilling the two popup tipup arm pivot points up to a larger size. Still not final size, but I decided that I wanted these to be perfectly interchangable, so the center to center distance between the various holes needed to be exactly identical between the two arms. It turns out to be quite a challenge to drill exactly perpendicular holes at exactly the same spacing through two thick parts. Anyway, after some time I had them matched.

The space for the goosenecks is .254...

...but the goosenecks themselves are .260. That's not going to work!

Setting that aside for now, I decided to trim down the tops of the gooseneck arms to allow for the popup function.

I had previously planned for the canopy to popup 1/4", but more recent checking leads me to go with 1/8" popup. That means I can make the pivot slightly higher than previously planned. I marked out the new pivot centera and scribed an arc for the top of the (trimmed) gooseneck.

Got this one filed down.