...the back pressure the engine needs to run right...

No.  No.  En Oh.  NO.

Even somewhat-modern fuel-injection systems in good condition can adjust the mixture enough to accomodate low-to-zero exhaust backpressure, and the benefit it brings.

A high flow cat and a FlowMaster Super 40 will give you a very deep note with out the deafening drone!

Is that a steel can on that one?

The thing a fuel injection system can't compensate for is the cam timing
and the way a cylinder charges, without a certain amount of back pressure
some of the intake charge blows out of the exhaust valve and down the pipe,
not doing anything but burning out your cat.

And if you think that the ECM will change the injection timing to prevent fuel
from going down the pipe, you need to brush up on injection timing and tech,
because even a sequential EFI injection system is not sequential at speed, the
injection cycle needs to start well in advance of the valve opening, and even
continue after the valve closing to actually inject enough fuel to get the mixture
right

Wild

I picked up a nice turbine 2525 muffler on ebay for $30 and slapped that on with 2" exhaust from just behind the cat on back and it sounds great minus a few cackles from the carb running bad very nice tone though.