I recently had to rebuild a Briggs 11 hp engine that had ran out of oil and seized the connecting rod to the crankshaft. To remove the aluminum from the crank journal get a small Tupperware container that the journal will fit down into, fill it with Muratic acid and let it set awhile. The acid will disolve the aluminum and with a little polish with some crocus cloth it will be as good as it was before. I have done this several times and also removed aluminum pistons from a 2 cycle engine that was run without oil in the gas.
NOTE: Don't leave the acid near any thing you don't want rusted. It's best to do it outside in the open air.