If I replace my stock lt1 crank with another stock lt1 crank, do I need to get my rotating assembly rebalanced? thanks in advance.

 

Factory rotating assys are all balanced the same, if any changes are made on the assembly line, weight is added or subtracted from the damper. So you should be ok droping in a factory crank, with the factory overbalance you should not notice a difference. If you are concerned about it, have a shop spin the two cranks in comparison to each other with a generic bobweight just to show that they are the same, that shouldn't be more than $75