just pound out, no?
If stuck at the 'flush' point, a pin punch to finish…
You're gunna leave the hole (newer gaskets cover it) so no special treatment beyond a dap of snot (grey RTV, black, etc) if U want it.
BTW: many R suggesting U leave the tails of the gasket above the case-break-point (about an 1/8 - 1/4 inch on each side) and allow the extra span to the other side to mate that gasket - apply more snot there (both sides of the 'break').
There's a thread on this final point (& ur orig Q). Some 1 even posted a url to his UTube vid W/his dad doing a rebuild that included this detail.