...earlier Packard Merlins used an American designed two-piece cylinderblock.
Are you sure of this? My understanding is that all of the designwork was by Rolls Royce. I've seen enough misinformation about Packard to be very sceptical of these sorts of claims.
A common fallacy is re-drawing (for Packard production) equates to re-designing. There are plenty of reasons to re-draw, including internal company standard use of first-order or third order projections, dimensions specified in inches and fractions vs. metric inches (inches and thousandths) etc. etc.