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
Packard had to redo the drawing from the UK first angle projection to the US third angle projection and include manufacturing specifications in US terminology. Packard also had to manufacture themselves all the necessary taps and dies to produce the UK threads.
Packard also provided a lot of information to Britain about the metals to use in the big-end plain bearing shells, at the time this was very secret stuff and even now there is a lot of incorrect information about
RR used lead bronze with lead indium flash whereas Packard used silver with lead indium flash, the Germans thought that the inclusion of indium was an impurity remaining from the smelting of the other metals, a finding I thought odd seeing the benefits of indium in bearings were published in the popular US press in April 14th 1938 (Aspen Daily Times).
There was NO material difference between a Hillington engine and a Packard one if you excepted the makers plate
Reference books cite that there were differences, engines supplied to Curtiss (P-40) and North American (P-51) used SAE No. 50 prop shaft splines while engines for the UK retained the standard SBAC spline. The supercharger drive on the two stage engine was changed from the UK Farman to the Wright patented epicyclic, magnetos were Delco (interchangable with the UK BTH), and Bendix injection carburetor rather than the UK 'g' sensitive SU.
Did you know the majority of US Sherman tanks were powered by Merlins? Well sort of if you stretch things a bit, Ford USA was initially approached to produce Merlins before Henry Ford declined, so it went to Packard. Henry set out to develop his own V-12 aircraft engine using the Merlin cylinder dimensions and configuration, but using automotive practices in certain areas, side by side con rods rather than blade-fork, cast crankshaft etc. For the Sherman tank they removed the middle four cylinders to produce a normally aspirated V-8.