I welded a steel pedal bracket to a cast iron 53 bellhousing for my pedals on my 46 to bolt to. Heated the cast iron up with a torch around the weld area so it would not crack when welding.
May work the same for welding the crack in your block.
Mark
1946 1/2 ton - 1962 "261" 1953 1/2 ton 5-window - "235" 1955 1/2 ton - 55 "265" Corvette motor 1959 1/2 ton Fleetside - "283"