It was Hooker himself. As a self-confessed - after Hives' initial comment - "not much of an engineer", he assumed that RR were the best.
Packard are very unlikely (I hesitate to say didn't as I don't actually know but I don't see how it could be possible) to have used the Ford drawings as UK and US drawing projections are different. Packard must have also produced their own drawings and although it would seem logical or even obvious for Packard to base theirs on Ford rather than RR - as the hard work had already been done - I've never seen anything anywhere about it either way.
The skewgear failures, IIRC, were caused by one company assembling components in a different order. No problem, all the tolerances were fine and there was apparently no reason why they shouldn't have done, but it didn't work.
I've never read about anything useful Leigh-Mallory did...