A lot of people forget that the RO/WO cars weren't built until March of 1967. Sox & Martin started the year out with two cars...a 440 GTX (White interior, bucket seat car), and a plain Belvedere II.

I've heard that the Belvedere was an original 383 car, but have never confirmed. The Belvedere was raced as a flat hood Hemi car at the AHRA Winters at Beeline, and the NHRA Winters at Pomona. There are numerous photos of this car. This car was raced as a flat hood car, a Hemi GTX, and an RO23. You can identify it in the photos as the Belvedere emblem on the fender was replaced with a rectangular Hemi badge (typically found on the lower fender). I believe this car stayed at Sox and Martin through 1968. I know they were contractually obligated to keep one '67 car into 1968.

The 440 GTX remained a 440 car throughout it's career at S&M, they did add the Belvedere trim to the GTX. It remained a 440 car after Sox & Martin sold it. This car always had the GTX emblem on the trunklid (right corner), even after it was sold.

The RO23 car came a little later in 1967. This is the car Dave Strickler drove at Indy. They didn't keep it long. Not even a year.

If you find pictures of the cars at Indy, the Belvedere was #716, the RO23 was #717, and the GTX #718.