Yes, I have the same problem. I need to alter my traffic. Somehow, for a fifties layout they don't seem too out of place, as I can remember that in the fifties there actually were loads of pre-war stuff still on the roads, alongside the new Morris Minors and Austin Devons, etc.
In fact my first two cars (in '62 and '63) were both pre-war. A '38 Austin, and a '39 Morris 12/4 saloon.
But after the introduction of the M.O.T. Tests, pre-war cars became very scarce.
I would also like to change my traffic to a later time.