Armour plate ex Mildenhall

This part was sold recently on eBay as Lancaster engine subframe armour.

I have been cleaning the part numbers and can see a few more letters and an inspectors stamp.

The numbers are numerous and are:

PP1284-1
1759A
2609DY
GP75P or G175P

DC or D6

Circular inspectors stamp with number 2 and letters S and possibly B visible.

Due to corrosion not as easy to see as on aluminium. Very similar style stamps to a Beaufighter plate that I have.

Any confirmation on aircraft identity ? Lancaster, Stirling or other ?