Just an engine, if it is usable it is good, numbers don't mean crap. The X's and all are a good conversation piece but if you don't like them, grind them off or have the machine shop mill them off. As to the "special acid".... unless you are with the FBI forensics team I doubt you are going to be getting it and using it, this isn't a gun with filed off serial numbers found at a crime scene. That said, if it were machined off and restamped very doubtful that anyone would ever be able to recover the original numbers or even care to try to.