If your truck isn't already equipped with 2 upstream o2's the eec is only seeing one bank anyway. It has no way to adjust fuel to two banks, so it doesn't matter which side you put it on, it will work fine (but read exception below). Also, if you ever get a CEL, the code will default to bank1-right side, but it could be either causing the CEL. This makes trouble shooting a little harder on one upstream o2 sensor trucks because it doesn't distinguish banks.

Just fyi though...the factory uses a little connector pipe right before the cat on the y-pipe to read exhaust from both sides.

The only way putting in one bank could possibly hurt you would be if the other bank is running real lean and it is not detected in the exhaust because the o2 is located way upstream in the other bank. Personally I would try and get exhaust from both banks from an H pipe.