Are All 340 Blocks the Same?

As stated most 72 and all 73 340 had cast crankshafts. 68-71 were steel cranks. One of our vendors MRL performance from his experience, has stated that the later blocks were better than the early blocks as far as core shift. To answer the rest of the question everything is bolt on same save maybe the 72-3 crank, balancer and flywheel/converter since they are externally balanced.