My engine is mounted inverted and it flys great on either side (inverted flight or normal flight) as far as opening the fuel passages I don't think is necesary the only thing we do is to lift the fuel passage needle lever located underneath the diaphragm just a bit so that is not even with the carb's frame, by doing so it lets more fuel to flow through, also the low speed needle needs to be more open tan usual about 1 full turn, Also I would suggest you use your 20% nitro and 12% oil glow fuel and mix it with an equal amount of methanol to make it drop to 10% nitro and 6% oil then mix a 1 part of that blend with 2 parts gasoline that contains 3% oil and that will make a mix that will contain 3.3% nitro, 3% oil, 28% methanol and 66% gasoline (roughly) you should keep the nitro and oil content between 3-4 %. Try it on your poulan 42 and let us know how it runs we are curious to see how it performs on a bigger bore engine.
Being that you already have a mix of glow fuel with methanol I figure that you have a mix of about 6.6 % nitro, 4% oil and the rest methanol if you mix a 1 to 1 ratio with gasoline it will give you the 3.3% nitro, 2% oil, 44.7% methanol and 50% gasoline you would need to add about 1.5 % oil to make up for the dilution and this blend also works very well specialy on the 18CC engine. if you take 1/2 a galon of your methanol/glow fuel mix and 1/2 galon of gasoline you will need to add 1.92 oz of oil to your new blend.