327 heads doesn't really mean a lot. What valves and combustion chambers do these heads have. From a performance standpoint that's what matters.
If your advisor who says you'll get more with the 327 heads knows their stuff it probably means you have some of the better 327 heads. A lot of 350 heads won't be any better and could be worse. On the other hand some of the later 350 heads would be much better.
What compression ratio are you going to run, what intake system and what cam. Those decisions will make a lot of difference.
