You can always sonic check the block. If there is enough minimal wall thickness to build at that oversize you are all set of that is your preference. If there is not enough then you can pursue the sleeve. A good shop should give you an honest opinion on your block given the crack and your intended plans? What are they telling you is the best course of action given the blocks current condition? Sounds like they build high horsepower engines. They are likely to have seen cracks before.