TBM is as good a place as any to stuff. I've ordered from them and had no problems. As for tank size, you dont need as big a tank for gas as you do for glow, TO A POINT! I run 24oz in my G62 - 62cc, DL50 - 50cc gets a 20oz, US41 - 41cc gets a 18 or 16 oz. Just a speculating on 26cc size, I would start with 10 to 14oz and see how it goes. I dont know. I set my timer for 10 minute flights and thats how I size my tanks. I just dont like have a lot more fuel than I need. Just a personal preference. When it comes to bigger, 80cc +, I have no experience. But then again, there are not many glow engines that size I think.
Edwin