A few thoughts inspired by some other sites...

The OS 46 LA seems to need less modification to run a nice 4-2-4 mode than the LA 40. A head gasket or two might be helpful. The LA engines run nicely on 10-11-11 fuel - which translates to 10% nitro, 11% each synthetic and castor oil.

Almost all mid-price-range OS glow engines are designed for the RC Sport user, so they have a broad RPM range in 2-cycling, and peak power well above RPM used in stunt. They run simply and well in the lower part of their 2-cycling range, again, at higher RPM than 'classic' (read iron piston in steel cylinder) stunt engines did. Lap times are regulated by prop load: pitch relates pretty well to airspeed, diameter to 'burden.'

As the LAs, and several other AB* engines, are based on running in their upper 2-cycling RPM range, too much diameter can cause them to overheat, and that can cause erratic in-flight quirks. So, a fairly flat pitch prop, with diameter that allows the engine to unload comfortably, may be more consistent - and kinder to the engine - than the traditional lugging a high-pitch prop at around torque peak RPM. (Most of our engines peak torque between 9.000 and 11,000 RPM. Power - horsepower - figures from torque times RPM with several other factors, of course.

With the upper-mid RPM range, RC Sport-intended engines, just riching them to 4-cycle takes them too far down their RPM range to give useful and consistent flight performance, unless the correct mods are done. That can be expensive, if ordered up from a specialist, or if parts turn out damaged by less expert work. Unless you really MUST have the 4-2-4 sound, you can get a lot of good flying in with an essentially stock 'modern' engine running 'wet-2' mode. (That is, a low, clean 2-cycle all the way through the flight, but with plenty more RPM available if you lean the needle further.) The power is amazing, as you're working the engine nearer to what it was designed to do.

Just some ideas to consider...