Hi Pete, I did it the way you describe, lowering the block with the pistons fitted, I wasn't aware of the other way to be honest
It does take two pairs of hands, we lowered the block with the two outer pistons at TDC & the other four at, or near BDC & fed a piston in each. It gets a bit more difficult with the inner four pistons as you have to feed in two pistons each at the same time, but if you're patient & careful it is possible. The only thing is in the manual it states to position the rings at even intervals for optimum compression, which isn't possible with this method, but they rotate in service anyway