I have never replaced the whole cowl side so I don't have an answer for you. But I do know that in dealing with reproduction sheetmetal I don't care where you get it, it is going to need work to fit. The amount could be not a whole lot to so much you might as well make it from scratch.
It sounds like you have one that doesn't fit, is that the case? If so post some photos and let's see if we can help you make it work.