Great looking Plymouth! One of my favorite cars and kits.
As far as the wide whites, the look is a matter of opinion but if you want to make it look like it would have on the street in 1964 it has to be narrow whites. Narrow whites hit the streets with the new '62 cars and by '64 nobody used the wide ones. Tires didn't last very long back then and by about halfway through '62 you seldom saw wide ones. Of course, wide whites could be had dirt cheap so many of them got re-capped into cheater slicks!