From 67 to 70 there were 2 trim levels above what was provided on a base no-option truck.
Mid level trim was simply "Custom"
High leve trim Level was "Custom Sport Truck" or CST
GENERALY (There are different things provided through the years) "Custom" Included upgraded iinterior door vinyl panels and arm rests, Color coordinated vinyl floor, Chrome inserts on the dash knobs, Extra cab sound insulation, Upgraded bench seat with cloth inserts. Outside you got chrome window and vent trim and "Custom" badges.
CST option includes everything mentioned above plus color-keyed carpet, Cig lighter, Vinyl imbossed bench seat (Buckets in 67) Chrome front bumper, Trim on the pedals and "CST" badges.
They are distinctly different comfort and appearance packages.
In 67 and 68 anyway the side chrome trim was an entirely seperate option. Many Customs and Most CST's included this option. Wheel cover upgrades were also a seperate option too.
In 71 the CST package was dropped for the Cheyenne and Cheyenne Super packages. The Custom package continued through to 72. I'm not really sure what you got in these packages in 71 and 72.
To add to the confusion, No suburbans could be ordered with the CST package, just the Custom package. CST (But not Cheyenne) could be orderd on any 69-72 Blazer.
There's no such thing as a Cheyenne Blazer or a CST Suburban
