The iS came on its own ring mount already fitted, which was identical to the supplied one in the kit, except it had 11mm holes that the mounting bolts went through. I had an engineering shop make some sleeves to suit, which cost a carton of beer.
As for the cowlings, a fair bit. Mostly due to the exhaust. Top cowling is straight forward, remove air intake scoop and fibreglass. Bottom cowling required shifting the bottom cutout forward to accomodate the muffler. Also a bit of cutting/widening around the scoop for the radiator, as it sits differently due to the exhaust.
Also made up some stainless radiator hoses, because I was concerned about how close the exhaust pipes would be to rubber hoses