[Pathfinder]

I'm embarking on a Lancaster artwork. Strange as it may seem, in all my years as an aviation artist I've never actually done this aircraft!

Anyway, I'm depicting a Lancaster Mk III.

My first question:

1) Is the MkIII the same as the BIII?

2) I believe the MKIII is externally identical to the MkI?

3) As these MkIIIs had Packard Merlin's, where as the MKIs had Rolls-Royce Merlins, were the engine housings/nacelles any different? Profiles seem to suggest they are externally the same.

Thanks in advance