Jonathan,
A Mark 5 with the frame number 11355 first appeared in the LDMCC machine register in 2001. At that time, it already had engine number 8944 - so your engine and frame have been paired up for at least 16 years. It is a puzzle as to why your engine number has been restamped, as it doesn't match your frame number, and it's original frame (8944) apparently no longer exists.
Regards,
Eddie.