First of all - welcome to sohc ownership. You won't regret it as these are great old bikes.
Assuming that you are in the UK and it's a UK model, a '79 will be a K7 as that was the last of the sohc bikes sold here. The dohc was lauched here in '79 as the KZ - look at the engine and count the number of camshafts.
If it has one - post the frame and engine numbers here and we'll find out the exact details for you.
If it has two - resign with red face and hop over to
www.cb1100c.net where I'm sure that you will find someone to help...