Ah, your V8 is a flat plane crank
What BBT says is correct - the lengths and diameters of the primary pipes (i.e. up to the first join) is the most critical thing, and they are usually designed to improve scavenging at a certain rpm by 'timing' the reflected pressure pulses so that a cylinder has a lower pressure in the exhaust just behind the valve, which will help exhaust the cylinder and also help, with a bit of valve overlap, improve the induction on that cylinder too - a very simple form of pseudo forced induction.
The silencers and mufflers have much less effect on the system (though appreciable gains can be made with freer flowing mufflers.
For a flat 6 I'd guess that you'd have a 3 into 2 into 1 on each bank, maybe with crossovers to aid the scanvenging, but that will depend on the firing order and crank design. A 3 into 1 (or 6 into 2 if you like) would be another possibility, but you'd probably tend to find it less than perfect as the scavenging would be less efficient.
As for multiple ends, that is purely cosmetic. Most cars will have only one or two 'main' pipes running down the car, and the split at the end will do nothing other than change the noise and styling. The effects of backpressure at this range from the engine will be minimal. The FZ being rear engined will of course have a shorter exhaust system, but I can't imagine it would have more than two main pipes, so the need for four exhausts would just add weight and make the car even more tail happy.
But ricers know best...