I don't get this whole engine builder thing. If you would have given me your 530hp engines, I could have shown you an engine pull that would show those VERY SAME engines to make at least 560 horse. Dyno's only report their results based on variables set by the user.
In other words, you can make a dyno say what you want. Period.
As far as builders are concerned, I still don't understand why they don't tell you 530hp and then deliver a miraculous 550 hp! Everyone would be happy then, wouldn't they?
Personally I don't give a sh*t what the dyno says, it's how much faster the boat/car,lawnmower, whatever, turns out to be after the motors are installed.

Now, if I bought parts that weren't actually in the motors, that would be called fraud. Different ball game.

I would have the shop buy your heads and you buy the darts and walk away happy.

So how much power, 574hp? did they make with which Darts?

Unfortunately it's quite common for the actual price to be quite a bit higher than the quoted price when it comes to engine work, not always or entirely the fault of the shop. I guess the end result will determine if the upcharge was worth it. If you stick them in the boat and it's bulletproof and turnkey, then you can say to yourself, hey it only hurt while I was writing the check. I hope that's the way it turns out. Good luck. Dave.

530hp without the Dart heads...574 with the dart heads...54hp difference....

Now...next year?? 6-71 Mega blowers....should just bolt right on (or so says the engine shop).