Perhaps you might contact the PFA and place a classified ad for the engine in Popular Flying. Their website is
www.pfa.org.uk, which contains the contact details.
The engine might go rather nicely in other designs as if anything like the 220 Franklin 6 cylinder engine, it would be light for its power output.
I heard somewhere that the Franklin 4 cylinder engine might be back in production(?) so there might even be spare parts available, if required.
The prototype Sprite did suffer a crash, I believe a spinning accident and the design was modified to include a dorsal fin. I do not think that there was any suspision of structural failure at the time.
Anyway, the engine sounds like just the thing for someone's flying machine.
Best wishes
KZ8