My flying buddy bought a SK50 a while back. It starts and runs good. If you do a search you may find the threads that tell about the SK engines being ported/tuned for large props and lower rpm not small props that scream. That would seem to make the SK's just right for your application in an LT-40. Only time will tell if they will hold up in the long term.
That said you would not go wrong with the OSAX. I have two in use and they are top quality and worth the price in my opinion. Another you should consider is the Thunder Tiger 46 Pro. The TT46PRO is a proven engine for about the same price as the SK's.
Fred