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Rod Yeomans has covered valve issues in his review articles, so be sure to read those. Here is some additional insight from others.
Thanks to David Bakkers for sending me this information via e-mail. In David's own words:
While reading the section on your site about small block 'Guzzis and exhaust valves, I'd like to mention a modification I did to a V65 that I used to own many years ago.
I too burned out the exhaust valves after using pod air filters and a too lean fuel mixture, but Epicycle Racing (A Ducati specialist who used to be in Epping, NSW) had a solution. They replaced the exhaust valves, guides, springs and collets with ones from a Japanese bike (I think it was Yamaha XJ950). The valves had the same face diameter and length, but a thicker stem and were sodium filled. The larger diameter stem transferred more heat to the valve guides and never gave a day's problem.