RE: Suggestions for an engine I have
Your best bet it to put it where it really belongs - pattern ship. Most of the designs from the 1970s and 1980s were designed for speed (energy) and many will hit 100+mph easily when set up properly.
Even though it is the LS version, that does not mean much. The engine can and will unload on a slightly lighter prop, but there is no need to push it that far. Prop and pipe it to turn about 12,500 rpm with an 11x10 out front and it will get you all the speed you need.
Look for some of the older but larger RE pattern designs - Aurora, PA-2, T2A Mk II , Deception, EU1-A, Brushfire, UFO, XLT, Escape, Magic, Illusion, Atlanta, Citation, Bootlegger. Even a Compensator or Dirty Birdy will work, you will just have to build your own pipe-tunnel canopy. Quite a number of pilots use to fly Tipoare, Tipo 750 and Curare designs with RE engines - pipe along the side of the fuselage (or moded with the pipe slightly tucked in)
Suggestion: look in the Classic Pattern forum. Information on where to get many of these aircraft. Several are in re-production and available once again
With the right setup, the gear up, and the pipe/engine/prop matched - you will have yourself an extreme speed pattern ship.