You can just ground right to the block. But ground all of them so your reference is the same across all 4.

 

Thanks for posting, this is great information!

 

This is interesting. I have a pesky P0161 / P0160 combo that I cant get rid of. I have done all the 02 sensor replacement & swapping L&R, etc. Keeps popping up. My truck had the front driveshaft fail at some time in its previous life and the 02 harness has been fixed as a result. So I think it is wiring, pin or connector related. Would there be any chance you could post pictures of your fix? You have a lot more EE know how. Thanks.