You don't need to cut out the glass, just the bad wood behind the dash and then replace with new. You can taper back the edges of the cracked glass and when you get ready to place the new wood, coat it with resin and add a layer of mat, wet it out good and then put in place and clamp (lots of clamps) tightly. Once that has set up, go ahead and give the rest of the new wood a coat of resin and maybe a layer of glass cloth. Then on the cracked glass on the dash, just start filling in with mat until it is level or above and block sand it back down to smooth. Just my 2 cents and the way I would do it. It's going to be a job but you'll be happier in the long run.
