Keep things simple, my suggestion is check the starter first see if you have power the battery terminal on the starter. Could be that the solenoid took a crap
You can use your stock exhaust as a template to see exactly where the brackets should go to match, and as far as loud exhaust goes don't forget your using Stock exhaust pieces which have been approved in all 50 states already. The cops will not even question it .
The exhaust system should all bolt together and you could just use your existing O2 sensors. It is still possible to add a WB sensor if needed just like you did with the stock exhaust.
Have a thought for the original poster, you could also pick up the stock H-pipe from a 13/14 and the over axle and mufflers from a 11/12 gt500 and you would be upgrading from what you have now and no one would be the wiser. 11 to 14 have 2 3/4 piping, 13/14 have the best stock cats and the 11/12...
The top of the cats, closest to the manifold should be easily visible they are very close to the manifold so they light off quickly for emissions , you could use a mechanics camera to see the bottom of the cats just will need a good bit of extension. Don't be afraid to shake the headpipe around...