Dave
I know this much :
Block number correct
L58 = Dec. 5th 1958
CS = 283cui 290hp, = Fulie
Serial #5126, built around March 2nd 1959.
I've read that in generel engines built until 3 months before assembly date is considered to be matching numbers.
It can vary, but I'd say that the engine is good.
Being a fulie block, it's gonna be worth some good money if it is OK...
That is if it hasn't been restamped....
Someone please correct me if I'm wrong...
Regards
Bjarne