Here's what I would do. Take the 4 studs out, remove the conn rod by cutting it or splitting the case and re-assembling it without the crankshaft. Scrape the gasket off. Tape some rough grit emery/sand paper to a piece of glass and invert the engine start sanding away. Leave the paper/glass stationary and move/rotate the engine block. Move to a progressively finer paper once the worst of what looks like a raised gouge is sanded down. ( If I'm seeing what you see).