Another Casting Number Question

I have been on the interweb for an hour trying to decode my 360's casting number. Some of you gurus know this stuff by memory and I'm hoping for some help. the number above the starter on the block is 3418496.1.360.6 It's clean there and that's all the numbers. I know it's a 360 but I'm curious about the year since it is not the factory engine.