This is roughly what I'm looking at at the moment. Just cardboard so far.

Alright. Here's what I did. First a tube about 3 mm in length (adjust to fit).

 Then add a rather larger tube around the bottom of the existing 'belt' and a couple of quarter pieces outside of that. Remove the detail on the front of the 'buckle' and attach the Scibor piece. The upper most edges should just touch the lower curve of the chest armour.

 Glue the thing together.

 The shoulder pads are still something I'm thinking long and hard about.

 Primed. The new colour spraycans aren't perfect, but its a good colour to layer on to.

 Now I need to do the other two, and work out what to do with the shoulders...

More on what I've been working on. Below is a Space Marine Bike - first one I've ever owned, bought just this month. Inspired by the Forgeworld Outriders I couldn't help but modify the forward fairing (back part to follow). With more patience I could have made this less crude, but I was quite happy for this to look  like a field modification, like modern-era bolt-on extra armour for in-theatre work. It looks quite over-sized at first, but remember how big the rider is...

 Pardon the blu-tac.

I'll admit the rivets might be too much though. Below is an edited photo with the rivets removed. Anyone have an opinion? I suspect the 'without' version is better - this is still a bike, not a main battle tank - but I might have to finish one with rivets and one without before making up my mind.

Aaaand, Ultramar PDF. I promise they don't look quite so bright usually. Maybe I need a softer yellow after all.