I've got a metal Proton you can play with if you are interested. All the Protons have the side port.I really want to try a side port all metal abyss (?) second stage . If anyone would like to lend me one to play with for a bit I'd be most grateful, of course I'd pay all shipping costs.
On the names... Mares has always packaged a first and second together. They originally just used one name for the whole set. The all-metal second that we now call Abyss had a different name and faceplate depending on the first stage. It first appeared as the Voltrex and came with an MR12, the Abyss name came with the brand new MR22, the Orbiter came with the V16 and the Ruby with a V22.
When Mares abandoned the budget Voltrex version, the 16 first stage and the Ruby poppet, the Abyss name was the last version standing. It certainly didn't hurt that the Abyss version was the one that made it through the US Navy cold water trials and was used by Mark Ellyatt to set the solo scuba depth record at 313m in 2003.