Put a wanted ad in the swap meet forum "trucks parts wanted". I've used it several times successfully.
Also keep a check in the trucks parts for sale in the same swap meet forums.
Sometimes you can get an entire 216 engine as cheap or cheaper than you can get individual pieces so getting a full engine may be your best bet.
Depending upon where the crack(s) is/are it may be cheaper to just repair what you've got.
Shop and price all angles.
Good luck
Dave
