One concern would be the shades of white involved. Unlike Basil's hardtop (which I assume is painted to match the body) there are many shades of white, some of which may clash or make the adjacent white look yellowish.
I know TR4s often came with white tops on bodies of contrasting colors, e.g. my TR4 still had the original white top when I got it. Which brings up the second concern -- white tops may not age as well as the black. Even if kept clean they get a funk to them -- with some effort the vinyl of an old black top can be made to look almost good as new. Just my $.02 worth.