I have a 75 -455 standard bore,was running,spun a rod bearing.I have a machined crank .010/.020  and a new set of bearings(rod/main) for it. You should be able to get rods resized and new gaskets/rings and run it.With crank and bearings $850.00.   with a crank that needs machining and  no bearings $600. motor is from a 75 grand prix sj(motor is still together,i just pulled the crank out of it)