What I'm hoping is that the several ground pours together will act as a more or less solid plane (helped by sprinkling of gnd vias)
And that right there is the key. To avoid poor AC behavior from taking traces over slots, use the vias to keep the ground return path right close to the signal line, something like this:

- GndPlaneCont2.jpg (6.08 KiB) Viewed 459 times