Maybe the deciding factor is the tire you are running, also. I always run somewhat skinny bias-ply tires, because I like the look on a fenderless car better than radials. I have never run a panhard bar or dampener, and have had zero problems. Maybe with radials it puts a different hold on the road, and magnifies the shake some of you describe.

My '27 roadster is as basic as it gets: Dropped '32 axle, hairpins, '56 ford truck steering box, and it tracks right down the road. I'm running 5;60 x15's on the front, and it steers and handles like power steering.

But like the others said, it's easier to add it now berfore the pretty stuff gets sprayed on.