Casting number

The seller contacted me this afternoon. He said it is a 1978 360 from a donor car. He doesn't know the milage but said it ran good after setting timing and some other adjustments. He sent me a couple of pictures and said the engine was clean inside the valve covers without any sludge or old oil??? It doesn't look clean to me... Attached are a couple of pics. He is asking 550. I think 250 maybe 300 tops. What do you think? My plan is to build a 408.

Thanks