RE: Which engine coupler do I need??
First .. you need a flywheel .. ask seller if he has one that will fit that engine.
Second ... cut-off the flat part in front of the threads.
Third : Threads on engine are 1/4" x 28 .. collets in that size to 3/16" flex-cable should be easy to find.
(Aeromarine / Octura / Hydro & Marine) , best collet is one that has a step-down that will fit inside the flywheel.
You can buy the Octura in the Swedisch-[link=http://shop.miniracingteknik.se/html/flex_hex_1-4-28_gaengad_axel_till_3-16_flex_(476mm).705.html?osCsid=e313dfc192c8ab5b03 c214061e0f1418]webshop of MiniRacingTeknik[/link].