here are my thoughts on it:
the BB6 is a different beast.
the 300 (BB6) has a 4" bore, and a 3.98" stroke
the Barra has a 3.6" bore and a 3.9" stroke
the 200 (SB6) has a 3.865" bore and a 3.126" stroke
compare that to the 351 (SB8 ) of 4" bore and 3.5" stroke.
at a quick glance, the numbers look like the 300 should sound really similar to the 351, after all its a longer stroke, and has two cylinders less. however that is where everything matters: the two fewer cylinders means the engine is balanced differently, and even the power band shifts, as well as operational/practical RPM ranges. not to mention the way air flows in and out of the engine.
the SB6, although a smaller bore/stroke than that of an SB8, is closer to the pulse rate, and airflow rates of the exhaust at idle to practical RPM ranges, however, produces a distinct buzzing sound at higher RPMs, which is what gave rise to the slang name for the ford inline sixes: The Buzzin Half-Dozen. even with the best tuned engine/exhaust, that inline six buzz is still there, and is easy to hear when one is looking for it.
there are a lot of differences between an inline six, and a V8. the sound of the engine is just the start of the differences. they are completely different beasts from V8's, and often times, even the differences between the SB6 and BB6 makes them different enough from one another that they require different building techniques when building one up.
when looking at the Toyota 2JZ-GTE (2.99L) and the Nissan RB26 (2.5-2.7L depending on year) compared to the late SB6 (200 Ci/3.3L) when all these engines are tuned well for their respective applications, their idles are almost indistinguishable in tone and pitch from a 4.6-5.7L V8. but few enthusiasts would confuse these engines with 6.0 or larger V8 tones, no matter how the respective engines were tuned. and if the Ford Barra was added into the mix at 3.98L (243ci) it would be next to impossible to confuse it with an American SB6 or BB6 for anyone who was used to hearing either.
now all of these sixes have bottom ends capable of handling more power than they came with from the factory; and all of these sixes have their share of downfalls.
Exhuast sound eventually comes down to two things 1) how hot is it when it exits the tailpipe, and 2) what is the volume of air escaping? the closer these numbers are to each other, the closer their tone and pitch. however all sixes will have that quintessential buzz at speed.
the link below is a built '7 second Barra', I put it here to give a good example of the 'straight six "Buzz"' there are also a few drag passes of a 400 windsor in the same car to compare with
