I recall reading a contemporary account in an ancient aircraft magazine of the time that the Packard engineers were taken somewhat aback when presented with several tons of drawings for the Merlin that the dimensions lacked tolerance specifications - the RR machinists / fitters were expected to know such information when building the parts.
There was also considerable flow of information back to RR about improvements and metalogy. For instance, it was said that RR decided to electroplate the head studs to prevent corrosion but found that this increased the occurence of the studs fracturing significantly. They had not known about hydrogen embrittlement until then.
Packard also encountered oil loss because of foaming at high altitude (25000+ft) and had to devise an oil seperator on the crankcase vents (why RR had not encountered that was not explained)
Surprising what picked up as a teenager gets retained after this time...