Yes, I have fitted two shoulder harnesses in my PA17.
During my fuselage recover project I got brackets welded to the upper, rear, tube clusters (at top of rear cabin). "Y" harness end attaches to these new brackets.
I was going to do what many others have done and that was to wrap the "Y" harness end around the cross tube that sits just behind and above the occupants heads.
However our local UK modification approval org., the Light Aircraft Association (a bit like your EAA), pointed out that the tube wasn't strong enough to meet relevant European airworthiness requirement.
I can post some pics if required.
TonyN