The Monkees episode "The Monkees Race Again" aired February 12, 1968, and probably filmed a week or two earlier.
You can see the Goodyear stickers front and rear on the Cobra at various points in the film. This fits with a car that was on loan to Goodyear at various times during that era.
The number 13 is a piece of paper taped to the back of the car - look at 2:27 of the film. You can see a number 1 under the 13. Anybody have pics of the CSX2299 with just a number 1 when it was at Goodyear or SA?
The hidden number could also be a 4, which might make it CSX2601 with the 4 left over from Coppa di Enna. Although my money is still on 2299 as the water and air jack nozzles can be seen on the top of the fender at 2:25 instead of the side like CSX2601 would have.
Thanks for posting the film! Now my wife is going to be wondering why I am going to try and order a Monkees DVD.
Steve