Help dating vintage Harmon Killebrew bat, please

There is a 4 in the knob indicating 34".

I have Googled and googled but not knowing too too much about vintage bats I can't find one like this.

I'm pretty sure it's pre-1973 if I'm reading ebay articles and comparing pictures properly.

I am storing this away from the house as its a Christmas present for my son so if yall need better pictures i can get them tuesday night..

 

looks like it might have been a give away at a stadiums bat day...

 

From what i understand if the number is stamped in the knob it is a store bought bat meant to be used.
Display bats didn't have numbers

 

Yup, i checked my H&B Co Rusty Staub , and no number on the knob.....so you're probably right.