The general consensus around here is that ALL the Chinese engines are a crap-shoot. None of them should be used right out of the box.
I would say to get the cheapest one you can find, and put the money that you save into upgrading it.
From the pictures that I saw of the Diamondback Kalamar Hybrid bike, I would say that you'd have a hard time fitting the engine in that frame.
Print out this template to see if it will fit your frame
Provided by Zoombicycles Motorized Bicycles,80cc and 50cc Bicycle Engine Conversion Kits,Bicycle Motors,Bicycle Engine Kit Parts