The exhaust manifolds are just close to equal length (at least as far as the 360° firing pairs) with a bank merge of some kind, likely an X-pipe.
As far as sound is concerned, the F355's howl comes from an equal length merge between banks (a Y pipe of sorts) with a valve that opened up to bypass the main muffler section, something they'd learned with the wastegates on the 288 GTO and F40. The 360 doesn't have a symmetrical merge, nor does the 430, which itself doesn't even have equal length exhausts. The 458 has the bypass "inverted" so the mufflers can be smaller - this means the howl arises very subtly and incompletely (the pipes from the muffled route don't fully merge, they are just very close together), whilst the bypass is two separate routes (one for each bank), giving the more 4-cylinder sound it has in common with its two predecessors. The 348 had two separate runs entirely.
So the 355 was unique, although the approach is used on most engine configurations these days (just not normally with equal length headers), because merging all the exhaust pulses together usually makes it quieter.
A flat-plane 'Vette is pretty out there, and to see them going for the "exotic" feel rather than good ol' "domestic" - how bold.