The round end studs are positional and not necessarily press fit for retention. The center rectangular protrusion that is klenched down is what retains the casting. You grind/sand/break that rectangular klenched protrusion to free the broken casting. Hobby Horse as reproduced the Lionel tools used to do these types of operations. The ST350-13 klench tool in a press is what I would use to klench the new piece.
Similarly, the coupler is replaced with a tool die as well. You drill out (or equivalent) the existing coupler base (careful not to enlarge the draw bar hole). Note you don't need to try to find the 2332-74 coupler assembly... it is just the more common standard coil coupler 6TC-10 with a wire attached. Again, you would use one of roll klencher tools form the hobby horse collection to fasten the coupler to the draw bar.