Need help finding engine No.

[wombat2509]

Hello All
I have a '72 Capri 1600 it has a 691M block I am having trouble finding the engine no. .I have 2 spare 681 blocks & the no's. are punched into the block just above the oil gauge outlet it is not there on the 691.One suggestion was that it could be on a machined shelf on the top but there is no marks there either.

Does anyone have any other suggestions,this was one only 4 problems for a blue slip but seems to be the biggest if I can find this I will be on the road in a couple of weeks HELP