talon co2 questions

First of all i have been building crosman H.O. co2 guns for years. the talon has been in my sights ever since it came out. My only problem has been the expense of a scuba tank or pump. Plus the fact that i would have to drive for 70 minutes to get a tank filled. i have several co2 and hpa tanks. So i guess my question here is can i get better than 700 fps out of a 18″ barrel on co2, hopefully someone will say 850. Second is this an easy mod. and last but not least is the number of shots on a 20 oz tank really near 1000.