Take the A40 towards Wycombe. As long as you have a compass and know what the nearest large town/city is (and let’s face it, you aren’t going to mistake Oxford for anywhere else) you can work it out.
I’m actually trying to geographically place that road sign now. My guess is what is now the Peartree interchange just out side Wolvercote, Summertown and Kidlington.
The roads have changed a lot in the last 70 years. The A423 doesn’t even exist south of Banbury now, except for a tiny bit (about a mile) on the Oxford ringroad.
