had a '63 chevy ll with three on the tree and they are so crowded up under the front floorboard area with all the stuff beater mentioned, that the factory trys to help out by dropping the throw out fork down to a 7:00 o'clock position (viewed from rear)rather than the more common 9:00 o'clock position) to free up the congestion. When I chose to block and split the exhaust manifold I put the new pipe to the front of original. This way the original (left) side would retain the all the complete original plumbing, and all I had to fab was the new dual (right) side.

The new right side went from further forward than the stocker, down, passing in front of the front crossmember and under the engine crossmember and then turn back toward the rear. I was fortunate at that time the aftermarket exhaust folks were making a dual side tail pipe (for the '64 Chevy lls with the V8s)-it matched the stocker that exited just behind the rear wheel (it would have been a bear to fab-kinda like over the axle and around the bend-to grandma's house we go-but I digress).

All that to say that the new dual side was several (maybe 3-5 FEET) longer than the stock side. 2" to the 16" mufflers (same as '53 chevy cars) which were snuggled in a recess under the back seat area. The twin Smitty steels would come into their plate glass shattering RRAAAAP at different rpms--it would RRAAA out of one pipe and while it was beginning to PP the other side would start its RRAAAPP outta the other pipe like Stereo pipes with a delay pedal (beater knows what that is-kinda Sun record style). Sorta like you had twin sixes blasting away only one had a head start on the other.

So there is a down side to making one side with to (oops) too much length just to make the pipes come out symetrical (just another reason I dont like metrics). But if you are running some body and he has his windows down - he's paying for it, maybe to the point of backing off first!!