I have never rebuilt a big block mopar before, but my crank grinder guy, who has been at it since the late 60's, once told me the throws on BB Mopar cranks can often be off a little bit in relation to each other. He was telling me the other crank shops in town have crank grinding machines that do not correct the indexing between all the throws and only grind each rod journal individually without considering it's relationship to the next one down the line.

If your building a closed chamber engine having the crank index ground is probably worth it.