Thank you everyone for your advise its pretty much confirmed what I had suspected (but hoped was not the case).
My thoughts where lazy lifters and i was hoping to change these without removing the head. ie from the top with an appropriate tool.
If this is something that can be done, i will. If not, it will have to go to the local Bristol specialist. He can look at it when he has finished the 403 that he has had for over a year now
(long story)
As for the rocker covers, im unsure where they came from. what I do know is its the last 411 made so may have had some goodies added at the factory, or someone spent cash on aftermarket pieces.
Thanks again everyone, a great forum with some very useful info. I have learned a great deal reading through the threads.