440 duster. Need engine build advice

cast crank requires 1. a different harmonic balancer up front (it has an offset or holes drilled to counter the crank balancing if you look at it closely) and 2. a weight-offset torque converter OR flexplate in the back (tq with weights or bm flexplate with a cutout. not both. most normally use the B&M offset flexplate and a neutral balanced Torque Converter, since it makes purchasing easier, so you can buy a torque converter anywhere. The stock method had a neutral balanced flex plate but the torque converter had weights welded on)

forged crank requires 1. neutral balanced harmonic balancer up front, 2. neutral balanced torque converter and 3. neutral balanced flex plate. All 3.
you cannot mix and match ANY of the weight offset parts if you have a forged crank.
everything is neutral balanced.

now the big shocker. Pistons, Rods and Crank need to be balanced together. In addition, if it's external balanced cast crank the machine shop needs the harmonic balancer and flexplate/or torque converter) in order to do it right.

just weight matching the pistons and rods is not a complete engine balance. those are the first two steps.

here's an article about crankshaft balancing
http://www.carcraft.com/howto/ccrp_0803_engine_balancing/viewall.html