I heard a fantastic Rivera head last night at a gig I went to, although I need to find out what it was - It wasn't typical head shape, slightly taller than a normal head, rounded edges and slightly thinner - More like an oblong than a rectangle.
VERY punchy sound and had some great lead/shred tone - Jems that were being played through it sounded super clear, the 7 string also sounded good (Bands had two of the heads.)