If the engine number starts A14 then it's pretty sure that's what you've got. I've built an A14 with an A15 crank before (using what I had laying around) & A12 cranks do fit into A14 blocks, but the only time I've heard this done was with a compact speedcar engine where they used the A14 block with A12 crank, then bored the block to 79 mm to get close to 1400cc, which was the capacity limit for that style of engine. It was done to make a real screamer of an engine, which is what I was told was the result. Still, it's likely you have a common variety A14. Enjoy the extra power & torque you have, & any upgrades you do such as bigger carby, extractors, or cam shaft work just a little bit better. Don't fret that it's not an A15, because the difference is not that great. Again, enjoy what you have, & go easy on those gearboxes.