it doesn't really matter. The 38's MIGHT have worn bores for the throttle plates, The 34's MIGHT be a bit finicky to tune. Pick yer poison.
If you go with the 34's, get the Canadian needles and emulsion tubes so that you get adjustable needles for fine tuning.
If you go with the 38's, identify the year that they are so you have a good starting points for your jets/pilots. Many variations of the 38's evolved between 1970, and 1979, every couple years, the appropriate jets changed. Jet the carbs to the carb set, not the motor year.