how is it going to kill my power? it seems to me that it has increased my power greatly
Sure you added more compression, but it's a flathead you can actually get more power with a lower ratio than with a higher one.
Flatheads do not have a real good flow velocity any way, and when you start popping pistons out of the deck, you decrease that flow. Remember the valves are beside the piston not over top of it, and the air/fuel mixture has to travel sideways to the piston, instead of being dumped straight down on top of it.
2 years ago we took a 40 ci engine and just a couple hundred dollars, and smoked guys running 42's and 46's that was popping the pistons out of the deck. We had the same cams and carbs, and they all swore up and down that it had to be over 50 ci. On a flatty I like big chamber heads, and I generally like to keep the piston down in the bore about .010. We might not be the champs but the 40 ci engine was a top 5 out of more than 50.