Hi Dave,
Carbs are different brand: SP carbs are Keihin (39mm) and standard is Mikuni (38mm).
An easy way to tell is also to look at front forks. SP is fully adjustable with rebound and preload at top of forks and compression adjuster at bottom of forks. The '93 R fork only has 1 adjustment: preload at the top of forks.
Also, the SP has a different windscreen as well: a lower, endurance screen vs. the taller screen on the standard "R" model.
Look for a small, plastic air scoop that sits on top of the radiator. Only SP models have this.
Try taking it for a test ride if you can because if it's a real SP, it will have a tall 1st gear...good for about 80mph.
Just checked out the add and it appears to be in "OK" condition...not bad, but not super great either which probably explains why it's so cheap. Stock SP models that are SUPER MINT are easily $8500.
Full-on, "Works" machines with YEC Kit everything...well that's another story when talking about price.