On the question of which brand of belt. Most likely you are stock and won't have any slipping issues. I've yet to hear of a Bonneville with slip issues until there was a tensioner problem. The W body (GP/Regal) is the one with slip issues because they have less belt wrap.
With that said..I've modded and run Dayco, Gatorback and Gates. I'm now a Gates fan. They look and feel like traction tape in the ribbed area.
Thread and attachment fixed. Dan, what happened is you use a hosted pic (attachment) from another thread. Each thread must have it'* own attachment or regulars members cant see it. We as Admins can see it because we have viewing permissions to see any pics hosted by the server. Makes for a puzzle, Eh? Let us know Velo, should be all good.