ballanced crank question

You need to balance it, and the only way to tell what the bob was...is to spin it on the balance machine and then add weight till its good....then weigh the new rods,rings,bearing,piston,clips,pin , etc to compare.
Im sure if you knew what pistons were used before...you could come close and or be able to possibly lighten the new rods, if they are even on the heavy side to start.

as for removin old mallory to re use, sounds like you spend more that way if the shop would even try.lol