Is this a good 340 combination? How much HP?

Well if the deck height is really 9.0 inches allot has been milled off. Stock is 9.59-9.60 so approx. .060 is milled off. Completely filling the water jacket isn't good for a street engine at all. Means no coolant can now flow around the cylinders. It's my understanding that you only do that on a race only block. You can partially fill a jacket on a street car but I'm not sure how much is ok. Maybe if I'm wrong somebody will correct me.

That's a whopper of a cam too especially with stock heads. Unless your running a 4,000 stall and low gears it won't have much guts on take off.

I'd keep looking but that's just me.