I just a called Central Hobbies. The YS 91 FZ is out of stock and they don't expect the 1.10 until mid summer. Their prices are considerably lower than Pro-Build ($275 vs 260 Pounds!). I am thorn between the 4-stroke and the 2-stroke approach. I don't want to cut the nice cowl to accomodate a side mounted two stroke. Í don't know where to get a wrap-around header and a round pipe to use with a upsidedown engine, but I have an Iron Bay fuel regulator to "pump" the OS 91 FX if needed.