Help me fill my custom crosman .22 ratcatcher

[deadsquirrle]

Just bought this gun at a local trade show yesterday. Guy told me he ran HPA but it could also be filled with c02. This isn't my first pcp. ( I had a disco .22 I ran on c02) I sold the disco so that's why I wanted to get back in the pcp game. Can anyone tell me any specific info on this gun or what I need to fill it. I prefer to fill with c02 if that's possible. I have several c02 tanks from paintball guns that are 20oz. My friend has a bulk c02 tank that he can fill paintball tanks with. So as I look at it, c02 is my most economical choice right now.

I was told the power valve is adjustable. And I know that the breech is totally custom.  I've always wanted to build one of these guns, but I don't have any knowledge of the pcp versions, only the pump 1377's. Any help would be greatly appreciated. Pics below: