I would go narrower than 4" myself. I think the very wide whites (4") look better on old Buicks and Packards etc. I had a set of 2 1/2" wides on my 49 but recently replaced them with blackwall tires, black rims and stock hub caps and trim rings. I had a tough time deciding whether or not to go back to whitewalls which are not cheap, so went with the black. And frankly in my opinion and opinions of others, the truck looks better.
