Scott,

the link below shows a Mk II Lancaster of 115 Squadron, similar to DS673.

Serial Range DS601 - DS852 Lancaster BII

200 Lancasters ordered from Armstrong Whitworth Aircraft in 1941 and built as BII from September 1942 and October 1943 with up to DS627 having Bristol Hercules VI engines and the remainder Hercules XVI engines.

http://en.wikipedia.org/wiki/File:Lancaster_B_Mark_II_of_115_Squadron_RAF_1943_IWM_CH_19792.jpg

Mike.