What are the advantages of the Riblett airfoil over the Original Pietenpol Airfoil?
Assuming that the same wing chord is used for both, one technical difference between the Pietenpol and the Riblett is the depth of the airfoil.  The Riblett that has been used on the Air Camper is the 612 (or sometimes the 613.5), which makes it 12% (or 13.5%) deep.  With a 60" chord, that's a depth of 7 to 8".  The deepest section of the stock Pietenpol airfoil is only 6-9/32", which makes it roughly a 10.5%.  The offshoot is that a taller spar can be used with the Riblett, and in spar strength the height makes a great deal of difference because the section modulus goes as the square of the height and the section modulus is what determines bending strength.  A taller spar can be made lighter with proper design.  Another useful consequence of using the Riblett is that a deeper wing section allows a larger fuel tank to fit in the space between the spars.  The stock Pietenpol wing centersection can accommodate maybe 10 gallons, but the Riblett should be able to fit more up there.

I've attached a graphic overlay comparison of the Pietenpol airfoil with the Riblett GA30U-612; Piet in red, Riblett in white.  The 613.5 is similar but the differences are a bit more accentuated.

For performance differences, I will defer to both a technical treatise by Mike Shuck (on the airfoil list) and the flight comparison between two very similar Piets conducted several years ago and documented in the BPA Newsletter.  Very similar performance in all flight regimes.