bigsport,
Check out Servo City
http://www.servocity.com/index.html and track down your 9151's. I believe they said 4.8 volts only. A 16 to 20 oz tank is plenty. I ran a 16 oz on my G38. I'm using a 20 oz for my DA-50, and rarely use more than 11 oz. in a 15 minute flight.