Sadly, when Alfred Hitchock died and the books were reissued, they decided to remove the character of Hitchcock from the books and replace him with someone named Sebastian.
In one sense you can see why they did it - Hitchcock was dead.... but in another sense it was just stupid. Why not add in cell phones and computers while you're at it - something these books of the 60s and70s didn't have.
Why not just keep the setting of the books in the 1960s where they belonged?
I'm going to share a link from Amazon to purchase the first book in the Three Investigators series - Alfred Hitchcock and the Three Investigators in The Secret of Terror Castle. One of my favorites.
Obviously you'll have to buy a used, hardback version - but the entire set, or at least the first 20 or so, are worth getting.