looking at buying the spacers that have 02 bungs, not sure if I need 1 or 2

yes

steve,one on each bank for a more accurate reading.

If carb'ed you might want one on each side as some manifolds distribute fuel unevenly, thus you'd want to tune to the leanest side. If EFI port injected you can get away with using one.

if you have one,put it in the 5,7 side,thats if its not swap cam.and its always a good idea put the bungs in both sides so you can see whats going on.

If this is for an OEM manifold I have a brand new one that I never used. I have to move to headers, so it's a waste of time for me to tune the oem manifolds for now. It's this exact critter. Shipped for $65.
http://wagsengineering.com/products/...sensor-spacer/