I second the TT42GP for a good bushed sport engine. I've got one on the club's trainer and it's been through hell -- yet still puts out far more power than an LA40.

This engine has been over-used and well-abused, yet it keeps on ticking over like a well-oiled machine. It was siezed when I tried some 20% nitro fuel in it -- but suffered no apparent long-term damage. It has been driven into the ground half a dozen times but still starts immediately, has a throttle response that puts many far more expensive twin-needle engine4s to shame, and is just a lovely little engine.

It's also quite light for its power output -- if that's an issue.