Not sure about the rest of you, but the last time I saw a wild BEAST OF FANTASY MYTHOLOGY the proportions looked the same...
Seriously, the kit is fine an one of, if not "the" best monster kit GW has produced - and in a starter set to boot.
The pic in this thread isn't flatering to the griffon due to the perspective but there is nothing wrong with it.
I find it odd how as modellers, we all crave some dynamic plastic kits, especially for larger beasts, yet when presented with something as truly impressive as this (for as few pieces, dynamic pose etc), some choose to nit pick the hell out of it as if there are thousands of better alternatives.
On topic, nice conversion Merrick, have been planning one of my own since I first saw pics of the griffon but still need to acquire parts. Think your right about the left arm, it's not sitting quite right yet.