You mention a chainfall. Are you trying to drop the blocks on the pistons with the rods still on the crank? I tried that on a U and broke a ring.
If that is what you are doing, take the rods off the crank, put them in the blocks.
Then hang the blocks from the chainfall and drop them in the crankcase. When the rods get close, slide the rods down a bit to the crank and put the caps.