E79 Phila. Caramel 27 Scrappers (red backs)
 

I was just wondering how rare these cards are on a scale of 1-10 compared to the black backs and how many of the cards in the set have actually been found with the red backs.

27 Scrappers with red backs
 

Definitely a 10 if that's the high end of your scale. If you wanted an approx ratio of black backs to red backs I would say 50 to 1.

All cards have been found with red backs.

Spinal Tap's "11" amp is about right...

It is a brutal set to complete in red back.