Confusing engine data and casting numbers

[Geert]

Last year I bought a 1959 C1 Corvette powerglide here in Europe.
I was already aware that the engine in the vette isn't the original one and so I want to know where it originates from.
The car came with some engine data(test report from Engine Analyzer Plus from Tom Thayer) and the more i'm trying to find out where the engine comes from the more confused I get.

Tha data on the report is as follows:
Bore 3.905
Stroke 3
Displacement 287.44
258 HP
This could make sense since the Vette standard has a 283 and with an overhauled engine this could be a little more.

But, the numbers on the engine tell another story
Casting number 3970010
Engine suffix V0702XD
If I look up these numbers it seems that my engine should be a 350?

can somebody please help me out here?
Thx
Geert

 

[Geert]

Found another casting number near the bellhouse on the passenger side, I assume this is the casting date which makes it more confusing for me as it already was
5279 or 5278 difficult to see, probably 9 in the end, the number is set between two notches

I sure hope somebody here can tell something interesting about this to clarify all this.

Thx
Geert

 

[Geert]

 

[Gregkz]

Hello from over the pond,here in Wash D.C.
I could be wrong as I am learning myself.
I have the same casting numbers as you but my build date numbers are a little different.
I hope someone can verify or confirm this for you.I believe that those numbers are the build date.
5 being the 5th month,May
27 being the 27th day of the month
9 being the year the block was cast
So that being said you have to use the other stamping numbers from the passenger cylinder head deck to figure out the decade in which it could be.
69,79
Good luck
Gregkz