That's what I do. Keep the engine a little less busy. The tires on my P6 are on 15x7 rims [on the back]and are the same diameter as the originals. the rear axel ratio is 3:90.
The speed limit in 1938 was 45 mph. If you are going 45 mph on the freeway now, you're road kill.
An overdrive won't fit in the tunnel of the x-frame on a '38 without mods.
So for now, it's country driving on secondary roads. Still a lot of fun!
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