The race is over and it was a blast!!
Ghettocruiser was 100% right: "the rider with purpose-built homemade studs will win easily." In fact, when I showed up with studded tires, the race organizer took pitty on me and loaned me his bike! Lots of 1/2" sheet rock screws, lots of silicon sealant, an extra tube "liner" for when the screws work their way through the silicon. The traction is amazing. Two riders locked wheels in front of me and locked them hard. On pavement they would have been down, but with spiked tires, they were able to pull apart. Tire pressure did not seem to matter.