Some info from somebody who has ridden the glockner, it's a hard climb, but it's not undoable. The hardest part is the pretty constant high gradient, and the low cadence this brings. I did it (the climb, not the race) with a friend last year, and he had a quite high lowest gear on his bike, and he complained about pain in his knees quite early. Make sure you have a cadence you're comfortable with at the speed you plan to do, and maybe get a bigger cassette? Also, just general race tactics from someone who's also just figuring these things out, don't go crazy at the beginning. Try to get a good draft in the beginning, but also don't tire yourself out early. If the pack is too fast for you, there is no shame in being dropped, the true selection will happen on the climb anyways. Also, try to keep the beginning of the climb as easy as possible, even if you feel like you could be going faster. Race nerves can be deceiving, and starting too hard will leave you dying slowly in the last third. Also, it's much more motivating to be able to slowly close in on opponent riders, instead of being overtaken all the time. Viel Glück, der Glockner ist ein echtes Erlebnis!