Bob, I'm using the PEFA "70cc" canisters from AI, and a 3.5" header on my engine in my 33% Compsite-Arf Extra. The headers are basically the KS pieces, availabe from DA, and are merely a 90 degree elbow, 1" pipe on the end of that, and if you use the KS flanges available direct from KS the "drop" is just about right for that airframe, though you might want to add another inch of length directly off the flange before you hit the 90 degree bend.

Power with this header/canister setup is right at 6850-6900 with a Mejzlik 28-10 (on my engines), and to put it mildly the plane becomes a rocket. Setting CG with this setup is very easy, since the canisters are slid very far forward, helping with the CG. Be sure to put a cuple of 1.5" holes in the belly right behind the LG plate to help remove hot air from inside the fuselage.

BTW, a guy at my field has a ZDZ80 on a plane, and gets 1/2 the "gas mileage" that I get with my 110/canisters. He sets the timer for 8 minutes on a 32 ounce tank of gas, and lands with basically only fumes in the tank. I set my timer for 15 minutes with a 32 ounce tank, fly 2-3 minutes past that, and land with 5-10 ounces of gas in the tank, depending on how hard I was flying. Depending on your flying style, a 28, or even 24 ounce, tank might be sufficient for this combination.