I've had mine run right to the rear.
It's a bit tight on account of the Air suspension but as the others say side exits would be tiring on a long drive.
(As much as I like the V8 'rumble!) Plus I prefer the look at the rear.

I might have to adjust the silencers once I get the drive shaft in place to allow for suspension movement and the pipes just clear on full compression at the axle.

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.