It can definitely be done but you basically need to do a complete top swap, everything from the heads up and you will also need all the front drive accessories, belts, pulleys etc. It'll cost more to find a machine shop to machine the heads to suit injectors than it would to find some L67 heads most likely.
Once all that is done the tune will need to be played with, the stock ecotec has a compression ratio of 9.4:1 where as the L67 is 8.5:1 so the engine will not be happy with the L67 tune and the ecotec has much weaker pistons which will not like detonation. Detonation from a bad tune will also hammer the big end bearings and you'll end up with a spun bearing in short order if you are not careful. I've seen this occur on a top swap ecotec that developed a rod knock after we were led to believe it was a genuine L67.