I think that He can sing The Rain Song, Over The Hills And Far Away. Why didn't They do it? Because they didn't want to play it.
His voice is fine but he can't sing that high as he could. I think it's only problem.
I use Guitar Pro 3 and 5. I download tabs from ultimate-guitar and 911tabs.com. I always checked tabs and add my own corrects. I do it by ear. I think it's the best way above book.