First off sorry for this topic as I know from searching it has been covered thousands of times.

I have tried searching but cant find what Im looking for

I am trying to identify if the engine in my 1949 Chevrolet truck is orignal but I can not find the block casting number. On the block on the drivers side I see the number 1 a few spaces then the number 946.
On the Passengers side I see 3 then below it GM (I am assuming that is just the sand casting number). On the serial number plate behind the distributor it looks like the numbers have been rubbed off but I can definitely see an AA on the left then on the far right something more fuzzy such as maybe a bb or 66?

Based on the AA from the serial plate it looks to me like it must be from a passenger car of some year. Is this correct?

Can anyone steer me in the correct direction? It would be greatly appreciated.

On the head on the passengers side I see the numbers 887 with 3B below it. On the drivers side I see 3701887 with GM 6 below it. Under the valve covers I see CON 13 and F183 and a small casting number 16.

Again sorry for this same topic again. I have tried searching but have not found my numbers.