Did chevy ever have 3/4 ton axles that had 6 bolt wheel lugs, or were they all 8 bolt lugs?

yes, the 9.5" 14bsf is a 3/4t light duty and has 6 lugs.

and a 3/4t front is exactly the same as a 1/2t except the brakes are slightly bigger and they have 2 more lugs.