A good picture of the bumper would help.
From that picture that appears to be a 67-70 bumper.
From research of other threads.
That it is probably a 1970 frame from St. Louis.
Because partial VIN's are stamped on the frame.
The first digit on the frame would be the 5th digit in the VIN of the truck.
5th digit is last number of the year and 6th digit is Assembly plant.
Link:
https://gmcpauls.com/67-72_chevy.htm