I was mistaken- I knew I'd read it somewhere, and I was convinced it was in 'The Shadows by Themselves', but I've looked through it tonight, and it's definitely not mentioned.
Where I actually saw it was in a magazine series from the mid 70s called 'The Story of Pop'. It's in the fifth issue, in an article about The Shads called 'The Backing Steps Forward'. I quote:
"'Apache' was an outstanding record at the time; a simple tune played in a pure, almost clinical way, by the Shadows. Each and every note was clearly distinguishable, and the three other instruments blended perfectly behind Hank's guitar; a very professional, tight unit. The cause of the new sound was Hank switching to a red Fender Stratocaster that Cliff had had shipped over directly from the factory in the States. (Before that, he had been using an old black Vega, which was semi-acoustic, and a Nanturia solid-bodied guitar which he'd bought for about £30, because it looked 'moody'.)
No mention of who wrote the article.
Simon