You dont have to run straight pipes to run flamethrowers.
First off before even attempting to do flamethrowers, research research research. And then go buy yourself a fire extinguisher.
A few companies make full flame kits while others just make a spark box that provides a "feed" to the coils you mount back there causing the sparkplugs to rapid fire. You then have to design a fuel or propane feed system. When my vehicle was carbed I ran a 3way filter to two fuel solenoids, one closer to the filter, and the other back closer to the fogger nozzle.
The fogger nozzles were a good two feet from the sparkplugs in the tail pipes.
Just remember to keep safety in mind as much as you can if doing this sort of project. The results can be very cool but also very hazardess. If an officer of the law sees you doing this . . . you'll be talking about the cool car you USED to have lol.'
Research on google and you'll find some good starting info.
Bringing history and technology together.