The OS LA .40 is roughly the same power as many .32 class engines and some hot .25s out there. The LA is a tad heavier though (I think). A lot depends on what you're doing with the plane, of course. An OS .32 would pull that plane vertically out of sight easily. More power than you need for traning. Any of the BB .25-.32 engines will give you plenty of power with out a lot of weight.

Oh, be careful when shopping in the .30range. Some .32-.36 engines are basically overbored .25 engines. This makes a light-weight powerhouse, and is a good thing. The OS .32F is like this. Mounts and weighs the same as most .25s, but way more power. But some .36 engines I've seen are closer to under-bored .40 size engines, making them noticeably heavier than most .25s out there. Look up the weight of a couple of .25 engines.

Anything with a weight close to that would be fine.

I'd expect eventual structural failure with a .46 unless some serious reinforcing went on. And the added weight of the bigger engine and extra structure would likely change the way it flys enough to make it not a very good trainer.

(btw, I keep references the OS .32F because I happen to have 2 of them. I've done engine swaps between the OS .32F, the OS .25FX, and Magnum .25XL and 28XL as they share the same mounting bolt dimensions. The .32 out pulls them all easily. The OS .25 and Mag .28 are about even, the Mag .25 is slightly weaker and slightly heavier) (The Mag .28 is exactly the same as the .25 except for the piston and liner)