If you do go for a st or gsi bumper, try and get 2, then cut them offset, so they meet in the middle, that way you won't have to make a big chunk up for the centre section, will save a mass or work. Better off selling the cossy kit to fund your project, I reckon, unless they aren't worth much
Connect arches do the trick really well covering wide rims, but finishing them around the doors is the hard bit and you have to be a careful you can open you sliding door. Are you thinking of the Cycovan (blue cossy YB), thats got a Transit MK3 fibre sport kit, adapted to fit on it, if I remember rightly. Does look really good
