I heard him say that he was about 0.800 left handed, but perhaps he was being modest. You can't really judge from however many left handed shots he shoots in regular games, as they are probably well-suited for a left-handed position. If you are shooting left-handed as a handicap, you also have to shoot the "right-handed" shots lefty, and those aren't so easy.
I would bet that Ceulemans would beat most of the American players playing lefty. I am not sure of what he means by his average playing lefty...as it could mean that of the shots he shoots lefty, his average is what you posted or slightly less as Bob mentioned. Or it could mean that he averages that playing entire games lefty. I am not sure. Regardless, Raymond would beat most American players on just intimidation