hello mate
sorry i can't help with the diana, though i'm fairly sure it's a kids rifle.
the mk1 hawk was made between 1971 and 1974, i have had a couple of them, they came new with two removeable barrels in number one bore and number two bore with a screw that you turned with a coin ( from memory!), the smaller bore barrel always seemed better than the larger bore (underpowered with the heavier .22 pellet).
i had both barrels with the first one that i owned but only the .177 barrel with this one that i currently own.
here are a few pics of the rifle.
>>>hawk mk1<<<
>>>hawk mk1<<<
>>>hawk mk1<<<
>>>hawk mk1<<<
these were nice comfy guns to shoot but were a little low on power due to the low swept volume of the slim cylinder...
regards, john