Arnold Schwarzeneggar's recommendation in his body building book is 1 gram of protein for every two pounds of body weight. I think that was considered the standard in bodybuilding until the mass marketing of protein powders.
That's around the US daily protein recommendation of .8 grams per kilo (2.2 lbs) of ideal body weight per day. To find your approximate recommendation, multiply your ideal body weight in pounds by .36.
(Note that in setting levels, the U.S. generally finds the lowest amount at which no sign of deficiency has been shown to occur, then doubles it for a safe margin of error. This number is often rounded up, as well. So you can safely assume that there is no evidence of deficiency at .4 grams per kilo, but of course you wouldn't want to be right at the edge all the time.)
The WHO recommendation is .45 grams per kilo of ideal body weight. (That would be approximately your body weight in pounds times .20.)
Most of the sources I've found say 10% of your calories from protein is the low end of the recommendation, but no studies have shown a need for more than 5-6%; again, there's a margin of error to try to ensure that people get enough.
Dr. Doug Graham has been following a diet like Steve's for about 25 years now. He's 54 years old and is in great shape, but he's not a body builder and never lifts weights, and doesn't have that sort of physique.
For more of a bodybuilder type, check out Richard Blackman, aka Fruitarian One. He's bigger, but not absolutely massive. He's into strength and fitness, but not bodybuilding, per se. And he only eats fruit, for the last few years, which seems too extreme even to me.
fruitarianfitness.com
He's also on youtube as Kinteet, where you can see him executing some pretty impressive feats of strength.
YouTube - Broadcast Yourself.
I know Steve's read the China Study, and that, amongst other sources, provides plenty of peace of mind for the low-protein crowd.