How to tell matching numbers engine?

I'm looking at a 70 Swinger, Fella sent a photo of the build sheet, Reads LM23HXXXX, Color on Build sheet says TX9, ( Car is plum purple ) He said its matching numbers, He did send a photo of the year on the side of the block 11-11-69, what would I have to look at to see if it is matching numbers?
Numbers on the block? to numbers on build sheet?

Thanks for the help fellas.