Ok in the early days they thought that all they had to do was stop oil running down the valve stem through the collets so they put the oring on there to stop it running down the stem and into the guide then into the engine, now the new ones are a more positive seal that seals on the stem and on the outside of the guide which gives a much better seal.
Now its up to you if you put the o'rings on the top or put the later model ones on the guide, BUT remeber that the old heads don't have a groove on the guide to hold the seal ona nd if they come loose they WILL pump oil down the guide as the valve goes up and down.
I run the oring style and haven't had any problems , the guides are in good nick on that head so it should be fine mate.