How much more is it worth?

Are you planning on selling it? If not, then follow your gut on getting that old block repaired. Otherwise, I would keep it as-is as part of the car's proud and fabled history, crack and all.

Whoever is going to pony up top dollar for one of these well preserved/restored have a lot of choices out there. The fact that you have the original block, even though it is damaged, will give you one more thing to tip the scales in your favor.