Shekel,
Reuniting with an old friend such as the old 25 is a treat! Such a thing is very lucky and rare!
You might have some difficulty dating the rifle because most of the very early Dianas didn't carry the reciever date stamp (In fact many 1970's don't).
Try to get a picture of the rifle and send it to me at ZVP13@hotmail.com, I will forward it to Dr. Beeman and he can archive it for reference and possible use in his BlueBook of Airgun Values series of books. (No guarentee he could publish it, OK?) We could also post it here also and I'm sure the picture would be a huge benifit in identifying other peoples early guns!
Happy for ya!
ZVP