So far, so good. Working first to fill the cracks and get the dash back into shape. Like others, I've used the Great Stuff foam to fill the cracks. I stuck some galvanized wire into the largest crack over the center gauge since it's thin and has nothing else behind it. I put tape over the cracks thinking it might reduce the expansion and make it denser, but I don't think it made a difference or was worth the effort.
Side note: I'm a little surprised people have had good and/or long lasting results with the Great Stuff foam, given how much more compliant it is than the rest of the dash.
Trimmed off the excess and started with rough shaping, then continued sanding to try and level everything out. Shot a light coat of black paint to try and highlight trouble spots. It's looking pretty good: still some bumps to smooth out and I need to clean up the curve around the gauges. I'd like to get the small gauge housings a bit closer to round as well, especially the clock. Might be able to lay the first layer of glass by next weekend...if UPS can move fast.