Don't know if you would be interested in a quarter-scale V8 aero engine, but
Woking Precision Models in England has plans for a very nice one by Eric Whittle from barstock, four-stroke, air-cooled, glow ignition, which I am going to be doing at 2X the size...the thing will end up at about 7" in length, (and somewhere around 45 cc) which makes it just about the size of most of the quarter-scale ones I've seen. You can get a good look at it in color at wokingprecisionmodels.com . Can't really be called a quarter-scale, since it is a prototype, not a model of an existing full-size engine, but it's a beauty! You can also get a series construction article from Model Engineer if you can find their URL (they are a bit on the reticent side). Actually, the complete drawings are in the construction article, so you can save yourself 12 Pounds (almost $20) if you can get the article reprints. They are pretty cheap.
Best of luck! If you like the look of it and can't get the article, mebbe we could arrange for me to copy it off for you. :