Although the facia of the Ace Cafe has changed since 'The Leather Boys' was made in the early 1960's the location remains the same. Importantly the A406, or as it is mostly known; the North Circular road, has moved slightly.
In the film we see Reggie (Colin Campbell) race Pete (Dudley Sutton), possibly to Staples Corner and back to the Ace Cafe, they stop underneath a railway bridge with advertising Ferodo products. This remains more or less identical today with the exception that the line, which leads to Euston has been electrified.
Interesting, for me is that at one point the North Circular was what the M25 road is today, an outer-London ring road.
IMDB entry for The Leather Boys, link.
The Ace Cafe, official site, link.
Ace Cafe on a map, link.
A link to some other pictures I took at the Ace Cafe, link.
Wikipedia entry for the North Circular, link.