Not sure why you are worried about the value of adding a vinyl top.

Its a slant six car, it's never going to be worth what you put into it compared to one of the more sought after factory combos.

If you are buildng it for yourself, build it like you want it, not how someone else wants it If you are building it to make money on selling, then it really doesn't matter because, imo, adding a vinyl roof does nothing for the value and I sure wouldn't pay extra for one and if you got your money back on the asking price you probably won.