The Vin plate on my truck is missing and I need to find out what the vin is.

I have read on this forum that the vin can be found on the engine block just behind the distributor. I did find the " number" , but I think that this is the engine code. I used this number and looked at all of the Chevy vin decoders that I could find. The number is invalid as a VIN. It has a different amount of digits.

Can someone validate that the vin is the same as the block number?

The block number shows as a 1950 3100 216CID

Thanks
Rick