The top bolt hole is the only issue with some blocks. If you have a N1 block , then you will not have to worry about this top elongated hole. If you have a stock block, you will need to see if this intrudes into the water jacket. Several people have installed a N1 water pump, and then had water weeping from this hole. Check it, fill it if you want to be sure. I have used epoxy and a straw to fill it in. You could weld it up if you want, although be careful with warping.
These pictures show the differences in the impeller design between the standard water pump and the N1 water pump. The N1 pump has a backing plate that helps reduce high rpm cavitation.