The difference as far as I know is simply in the way the headers are built. Twisty style headers are more narrow, or closer to the engine block than the regular headers.

Here's a shot of standard headers


Here's a shot of twisty headers


Notice how the twisties are more backswept than the standards...

Thanks for the info Luckie! Now I see the difference. Although maybe a little less attractive, the twisty design still look like they might make a bit more low end torque. I'll have to further investigate that.

Literally the only advantage of the twisties over the talls is the increased room you get if you have a bench seat, I sold the standards to get some twisties because of "elbo room"...I hate the smell of burning flesh. ....

Otherwise, I would be willing to bet they run the same HP wise....

GT

The other thing to keep in mind is clearance around the headers.  If you have a narrow hull like my Hondo you might have problems with anything you choose. 

I only have 9" from the rear exhaust port to the inside gunnels  and with the design of the twisty headers making the rear tube stick out the farthest makes is almost impossible to use on my boat.  I just installed a standard set of Bassett BBC jet headers and you can see how close it comes at the third pipe (1" clearance)

I fabricated a set of small heat shields to help keep from burning the gel.

Hope you have a little more room than I do