Rob, with regard to the two different ignition modules, I think I've found the answer in the GXV160 workshop manual:
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It seems there were two different ignition units used on some GXV models: a conventional electronic unit (N type), and a capacitive discharge unit (A type). The small unit in my picture in the previous post was the N type and the large unit was the A type. I haven't yet seen an A type on a GXV120 - they may not have used them on that model. The alternative mounting points on some Honda cylinder blocks are for the A type, and may not be provided on GXV120 blocks, though they are on the GXV140 and GXV160 blocks.

The GXV160 intake ports remain unclear at the moment. The parts list shows the GXV140 having 16211-ZG9-000, which is the insulator shown second in your list, and the GXV160 having 16211-ZE7-000, which is the thicker insulator for a large square intake port.

The first insulator in your pictures is for the GXV120, which has a round intake port. The second is for the GXV140, which has a D shaped intake port. The GXV160 remains an unsolved mystery.

You probably know that the GXV120 and GXV140 have the same stroke and different bores. They share the same crankshaft, connecting rod, and many other parts. However they have different cylinder heads to suit the different bores.

The GXV160 (68 mm)has a larger bore than the GXV140 (64 mm) which itself has a larger bore than the GXV120 (60 mm). The GXV120 and GXV140 have the same stroke (42 mm) while the GXV160 has a longer (45 mm) stroke. It would be physically possible for them to share the same cylinder head.

So, thank you for that, your post has led to unravelling the matter of the two ignition modules. The matter of the intake ports and carburetor insulators remains mysterious.