I've got the ARF LT-40. I first flew it with an Irvine 39 which worked perfectly for this plane and enabled me to solo first time out (this was not my first trainer).

At this point it's worth noting that the Irvine 39 is about 2ozs heavier than the 46LA and is more powerful, although not as powerful as the OS46FX.

I bought an OS 46FX to go in another plane so I thought I'd put it in the LT to get used to it and break it in. I moved the battery back to keep the CG in the same place. When I made the change I noticed two things:
1. There was practically no difference in performance
2. The nose would drop noticably more when power was removed.

So, if you can find an engine that has similar power to the 46FX but is about 3oz's lighter, this would be the perfect match.

BTW. I am now running an OS FS70II in the LT with an 11x6 4 blade prop. This is an interesting combination that will pull the plane straight up almost out of sight, but I think this engine is too heavy for this plane.......