According to some of my books about the Royal Enfield's, the Meteor was the 700 twin that was introduced in 1952.
The 700cc Super Meteor came out in September, 1955 and was ready for production in 1956.
Among the changes for the Super Meteor was larger rod journals 1 7/16 dia to 1 3/4 diameter), increased fins on the cylinder head, increased inlet valve head diameter, Auto-advance on the Lucas magneto (changed to coil style in 1958),
The Meteor was marketed in the USA as the "Indian Trailblazer" which initially used the Meteor engine.
The Trailblazer got the Super Meteor engine in 1956? (source unclear on this). By 1957 the Super Meteor was being used for all 700cc twins including the Chief.
The 1957 Indian Apache used a "tuned Super Meteor" engine.
At least, that's what the books say, reading between the lines.