Hi Jack,
The letter that I have a copy of from Emerson says that only 5 Rhino's have been made. I got four of them (not from Emerson), the letter further stated he kept the 5th one.
Rumor has it that 2 more have been made. I know where 4 are at, how much are you willing to pay? I might be able to get one. The price will be in excess of $2,000.00.
As for a Viper 4, I know of only one that has been made. I have never seen one of these in person. Hence I don't think but a few were made. As at one time or another, just about every unusual Emerson has passed through my hands at one time or another.
Viper 2, several are out there. This will be the easiset peice to get.
Good Hunting Jack.
Les