I would bolt it to an engine block. Drill the end of crack to stop it, otherwise it will keep running while cracking.

I would V out two spots. One as close to the mating surface as possible without getting weld into engine block. The other midway. Make those welds on the one side. V out the opposite side and weld. Then V the remaining area and weld.

Like others said you will probably have to boil out the contamination in the porus aluminum.

Not a hard place to weld.