RE: Super Skybolt ARF
You don't need to do anything special to the tank for a YS engine. The pressure is considerably more that other 4-strokes, but not so much that you need to worry about it. On nice thing about a YS is that you can mount the tank back a bit to get it over the CG. In my original KIT Skybolt, I had the Smoke oil tank where the Fuel tank should be and the fuel tank behind it (Which places it at the CG). I'm hoping to modify my ARF to this configuration this winter.
As to mounting... I almost always use a horizontal mount. There are 3 reasons why I hate to mount an engine inverted:
1) Sometimes they don't run right inverted
2) It makes getting the Glow Igniter dificult to get on and off
3) If you have a nose-over with an inverted engine, your engine is what gets the most punishment.
None of these three things are major, but combine all three and I just find it much easier to mount it horizontal - As far as lateral balance goes, you'll need to balance it laterally anyway - Maybe they used more glue on one wing, or heavier wood - So as long as you have to do it anyway, why worry about the position of the engine?