If it was changed for that reason then it would be the other way, Merlins rotate the same way as US engines (right hand), the Griffon goes the other way (left hand), like other British engines such as Bristol, Alvis and DH.
I thought the P-40 with the Allison was right hand rotation? The propellers appear to be right handed.

Interesting point about the crankshaft Richard, wartime Griffons have a very offset counterweight on the crank, although the G58 crank looks more conventional.

Pete