Neil,
I used high profile valve covers that I got from Cobranda. They clear the roller rockers with no problem.
The only issue I had is that they are not available in black crinkle finish to match my air filiter cover. Nonetheless, I sprayed them with black crinkle paint and then used lacquer thinner to remove the paint from the ribbing and lettering.
Below is a thread where I posted a pic about a cooling system burp valve I installed and you can see the valve covers.
Cooling system
Tony