OD,
Here is a web link for you if you want to see what aircraft the O-290 has been used on.
http://home.adelphia.net/~aeroengine/Lycoming.html
Not able to comment on the reliability.
Other engines to consider would be the ubiquitous Lycoming O-235 (about 116 HP normally) used in Cessna 152, Piper Tomahawk and a bunch of other things. May be a little underpowered, but reliable. Need to remember that it is the only engine in Lycoming's current range which has manually adjustable tappets and so do need periodic adjustment. Lycoming's others engines have hydraulic adjusters and so automatically adjust themselves.
Some of the parallel valve Lycoming O-320's are lower power than most, coming in at 140 HP to 150 HP. Again known reliability as fitted to some early PA28-140 Cherokees, PA 22 Tri Pacers, Super Cubs and the like.
There is also the more obscure, like Rolls-Royce / Continental O-240 of about 125/130 HP. This was fitted to Rollason Condor, Robin HR200/100 and Reims Cessna 150's.
Finally how about the new 6 cylinder Jabiru 3300? This looks pretty well engineered, is a new engine with small frontal area and delivers around 110HP. May be worth considering...
