I beg to differ with Ed, but I have exactly the same aircraft and you can indeed use a calibrated dipstick as long as you recognize the limitation, specifically that it won't measure below 30 gal per side. Above that, it's very accurate. Most of my flights are over water, adequate fuel is more critical to me than for most other Skymaster pilots, and I spent considerable time researching the system and making the information available in the Fuel Supply Management page at
www.SKymasterUS.com
Other techniques, like supervising fueling and keeping close tabs on time, are critical, but for me the most important is climbing on the wings and using my dip tube.
Ernie