Thanks MARTINSR for more great advice! I can see why sanding was such a chore considering the choice of fillers, but I'm one of those "weird" guys that doesn't mind sanding (not saying that I love bondo--the idea is to use as little as possible). I see it as just one more aspect of the overall resto or rodding project. I get excited with every new area I start on my Corvair. Each job is bringing me closer to completion, but sometimes I wonder if I will be a little sad when that day comes, because I love the "roll up your sleeves and get dirty" type of work. Anyways, just my 2 cents!
BTW: Thanks for the sandpaper info!