I have several of the gyro and inclinometer units, and the magnetometer compass, somewhere. The gyro was a motor spinning a flexible metal plate. As the vehicle moved, the plate would flex, and sensing the plate's position gave a rough turn rate. The inclinometer was a little sealed cup with four capacitive sensing plates. I was looking into using this for a robotics application, but it was too big for an R/C car sized vehicle.
I'm surprised they had a gyro (the article also only mentions a compass, which makes sense to remove accumulated errors in heading). I would have expected the wheel sensors to provide data of similar quality as a gyro back then, without the cost.
