Going to be sending for a tune in a bit. Switching to Long Tubes from factory manifolds. Will be eliminating cats and the emmissions system. When I get the tune, should I have the rear O2 sensors tuned out? If I don't, will the SES light come on?

 

If you remove the cats, it will cause the after-cat O2 sensors to set codes/SES light for the missing cats. You either need to plug a pair of O2 "sims" into the O2 sensor harness connectors, or have the codes "tuned out". The sims are getting hard to find, since the EPA started charging huge fines for the manufacturers.

The other emissions components that tie into the headers are EGR and AIR systems. They both set multiple codes, and will need to be "tuned out".