I haven't purchased a BSA scout derby kit in a while, but what is the cost on them. If your just practicing you could rip the block in half and have 4 potential test drills, 2 per block, just use a short wheel base drill with the rears being 5/8" from the back. Drill it and if it's not to your liking give it a 180 and drill again. Just an idea.
Oh yeah... when you're done with the bad drilled blocks, save them. Use them for paint blocks, support blocks to keep the cars from rolling off the table, drill multiple holes in them to hold axles or whatever else you can think of.