I'm sure most of us here know Honor Blackman was Pussy Galore in "Goldfinger" and Alexander Knox (the Senator) played the American President in "You Only Live Twice"
Jack Hawkins and Stephen Boyd were both in "Ben Hur" they had no scenes together in BH. Future Bond actor Robert Brown (M in OP to LTK)played the galley master in same.
Let me add that, according to IMDB, Boyd was among the actors considered for the role of Bond in "Dr No". Hawkins and Boyd both played (and had a scene together) in "The Third Secret" (1964), which also featured Diane Cilento, Sean Connery's wife at the time. Also, Bardot and Boyd had both starred in "The Night Heaven Fell", back in 1957. It's a small world, after all.
Diane Cilento was with Paul Newman in "Hombre" witch had a plot much like Shalako Which also starred three time Sean Co-star Martin Balsam ("The Anderson Tapes", "Murder on the Orient Express" "Cuba") Years before Sean starred with Paul's wife Joann Woodward in "A Fine Madness" Lastly check this one: Sean Connery and Robert Shaw were on the Orient Express in "From Russian with Love" , Sean Connery and Martin Balsam were on the same train in "Murder on the Orient Express" and Martin Balsam & Robert Shaw were on a train in The Taking of Pelham 1, 2, 3
Lastly fellow trainjacker (Pelham 1, 2, 3) Hector Elizondo was also in Cuba