Valve Covers Stuck

I am rather embarrassed to admit it, but I can't get the valve covers separated from the heads on my 1975 R90/6. Yes, I removed the center bolt.

And, yes, I have broken a couple of fins.

On my BSA's all I had to do was offer a light tap with a nylon mallet and the cover would pop off. (Of course, there was a nice layer of leaking oil between the cover and the head on the BSA!)

Any suggestions will be welcome.

Thanks, Stephen

Steve, did you get the 2 other nuts hiding at the front and back inside the fins ????
That's 3 total if you include the main bolt. They are easy to miss.

Indeed, they are, and were, too easy to miss. I will hang my head in shame - but just for a little while.

Thanks,

Stephen