I agree with 68tpls400 - Since top and interior are black, the black stripe would be the best combo. It will actually look a lot better than you may think. I'm doing a restoration right now of a 68 convertible - Solar Red with white (ivory) top, white (Pearl) interior and I'm going to add a white Rally stripe (which it never had), again, playing off the top and interior. It always seemed to be missing something and I think the white stripe might be just the thing to pull it all together.

Good luck with it. You can always change the stripe after you win the lottery.

Come to think of it, if you do hit the lottery, consider painting the car white. IMO white with a black (or red) rally stripe combination looks great.