Mr. Jody,
Laminar vs turbulent flow is not a choice at this point in the exhaust. All flow transitions from laminar to turbulent at some distance, based on Reynolds number and surface roughness. In an exhaust tube like this the transition occurs within a few inches for smooth walls, so surface roughness is effectively inconsequential as it only causes the onset of turbulent boundary layer to occur a couple inches sooner.
You are correct that louvers on the outside of the flow passage will be less restrictive. it will also be less effective at reducing sound, so there is a trade. In this case, with a 3" tube ID, the vena contracta will still be around 2.25", given the boundary layer thickness, so the OP will have plenty of "effective" cross-section to have considerable flow. Certainly enough for 331cid. If he were to have say 540cid, thats another story
The spiral pattern is not likely to have any effect on reducing overall flow restriction, but may prevent strong wave patterns from standing in the tubing, basically causing a reduction in noise due to destructive wave cancellation.
Now back to your regularly scheduled programming...