If you can still find one, a YS-63 will fly that plane as well or better than the .46 2-stroke and still be lightweight. It is being replaced by the YS-70 however which of course would be even better.

Beyond that, any good .70-.82 4-stroke will be excellent. If you can find a discontinued OS .70 Surpass-2 it would be a great choice. There new ones would be too.