Yes it's an ETA 15 diesel, albeit with non standard venturi (the banjo is missingas well) and spinner nut assembly. Still should bring a good price on ebay if the rest of it is in good condition. Mostly good motors, and were used successfully in FAI Team Race before the Super Tigre 15D came along.
Made by the great Ken Bedford in the UK. "ETA" is a alphabetical Greek symbol used in Physics, the symbol is embossed on the front of the crankcase.
Here's what it originally looked like