Step 124. Having some difficulty from the diagram figuring out how to orient each of these four pieces. Can't figure out if the light grey nozzle is suppose to snap into the bracket shown in step 123. So far no problems except for this. LEGO needed a bottom view of the assembly.
You just need to slide each of these 5 sub-assemblies onto black/yellow axles. There are no further attachment points between this sub-assembly and the rest of the model.
Instructions suggests you need to point each nozzle toward next engine in outer circle (except for center one, which works in any orientation). You don't really have other options for orientation since parts you've put together on previous step limit positioning of the sub-assembly found in Step 124. And looking at the pictures from various reviews I found over the internet I don't think there is a good way of picturing engines from the bottom since colors are dark and pretty much the same.