got new headers in today but no up stream o2 sensor

i got my headers in today the only problem i have is there is no up stream o2 sensor on the longtubes there are some down stream but i didnt know if the up stream not being on there would be a problem not having it effecting my gas milage etc. and if so can i get one welded on

You can weld in a bung for it

Brand? LT's?

Pics?

If they are LT's then yes, the upstream gets connected at the collectors.

No down streams, they get turned off in a tune.

If there are no cats, you only need one set.