I hear you Tout! It would be news to me.
How about a "time line" check:
The magazine article was published in January 1966. So what month and year would the Tourist Trophy Race be run? Perhaps Oct, Nov or Dec 1965? Even earlier?
WAS Ken Miles in fact running an alloy 390 at that time? PERHAPS the magazine was "confused" about what K. Miles really said? Perhaps K. Miles DID make reference to the alloy 390 and the magazine assumed that he talking about the 427 engine in his car at the race?
'Cause you know, you can ALWAYS believe an article in a magazine.
Ernie