To answer the question in the strict sense, no, the Smoothie was "designed" for a Veco engine because that's who was supplying engines for Bob Palmer in those days, up through the T-Bird era. But a more useful answer is, use a modern reliable engine that runs smooth and burns fuel with synthetic/castor mix that doesn't make such a gawdawful mess on the plane. The extremely short snout on the Fox also mandates a very far forward mounting position, not the best idea.
I built a Brodak kit Smoothie and also an ARF Smoothie, with an LA40 in both. An even better choice is the LA46, which seems to produce a better stunt run than the 40 (and is still available new, which the 40 is not). The rather compact Enya 40 (new design version) would be a good choice. An APC 11.5-4 is a good prop choice and gives a bit more ground clearance than the 12.25-3.75 that also works very will. If you can get your hands on one, a Brodak 40 would be a really great motor, light and reliable. May be available used or by posting on this forum that you want one.
The Smoothie is a great-flying design and is good in windy conditions. Legal in OTS, Classic, and modern.