exhaust pipe diameter for a mildly modified 340

My 340 runs stock manifolds and it likes good exhaust systems.The difference between the very best system and stock setups on mine might be .15 and 1.5 mph so it is not much to worry about unless you need very tenth.
What does matter is the driver's side exhaust pipe out of the manifold. There is some serious power loss and for sure, I'd fix it. Tom Swope at Accurate can bend you 2,5. pipe to get aorund the starter and torsion bar and that is worth doing. The stock set up is about a 2" pipe squashed in half. It has to hurt although I can't say how much since mine has always had a homemade big pipe on the drivers side.