502 vs 454 crank
 

According to Dennis Moore's book, the 454 crank is balanced different than the 502 due to the piston weight difference. Can't this balance issue be corrected once the rotating assembly is balanced all together?

The 502 and 454 cranks are blanced differently and wold be a problem IF NOT REBALANCED. You can rebalance for almost any change, just DO IT!!!:D

Rebalancing
 

So when I get the rotating assembly balanced and then completely balance the engine, the 502 crank in the 454 engine would not be an issue right?

If you get the rotating assembly balanced then it no longer matters. Both 454 and 502 assemblies use counterweighted flywheel and damper.

Yes the crank just rebalance , note the flywheel and harmonic balancer are different tho and cannot be interchanged

Nay, 502/454 do share damper and flywheel. External balance factor is required, but is identical for both units.

Balancing difference is within the crankshaft counterweights alone.

454/502 use EXTERNAL balance factor on damper and flywheel while 366/396/402/427 use INTERNAL balance factor with NEUTRAL damper and flywheel. Many aftermarket cranks offer chioce of balance factor.

GM factory forged crank for 454/502 requires EXTERNAL balance.

oops I stand corrected 454 and 502 are the same, I did a conversion last winter 502 long block using 454 accessories but the flywheel change was due to the change from a MKIV to Gen 6 crank not due to the 454 to 502 change :)