Since it's "raw" foam you can't use it for any sort of structural use. And for very casual flying you don't really need THAT big a wing. Smaller wings would make the "flying cylinder head" look more dramatic. Provided the "block" isn't that heavy I'd say you could easily get away with a 4 foot span wing and around 480 to 500 sq inches and use a simple top and bottom sheeted 1.5 inch deep box fuselage that the head sits on. A .25 size engine would provide the power quite easily if you figure you can keep the weight down to around the 3 to 4 lb mark. And it would be more dramatic with the model parts being visually small compared to the head. If the head is quite light I'll bet the engine and wings could be even smaller yet.

Now... if you have access to the original tooling that made up this head could you not cut out a whole V8 block? If the block itself can be made light enough I'll bet you could use that 91 and the Tiger wings and tail and have a whole flying V8 by scooping out some of the foam to allow fitting a simple box that holds all the parts. The prop would just HAVE to be where the cooling fan normall sits but perhaps place the prop slight further forward so the blast doesn't stagnate against the front face of the block. Yes it would be inefficient but I'll bet it would fly well enough to do what you're after. And imagine the looks!