This is a really fluffy article. It doesn't discuss how they got the ignition timing right, installed an ignition coil, distributer or coil packs. Modern gas engines have about a half a dozen electronic sensors that deal with the internal position of engine parts or fuel air mixture. Maybe some sensors from the diesel were reused and they just used the diesel timing to fire the spark somehow. Anyway it is not suprising it knock or ran rough. If they installed correct electronics it may have ran much better.
Btw. the reverse, converting a gas engine to diesel is much harder if not impossible for practical purposes.