I don't think you can entirely eliminate bump steer with either a panhard bar or a deadperch because they both swing on a long arc which changes the effective length with the up and down motion. However, I would think either would GREATLY REDUCE bump steer compared to none at all. I think you can see in my picture a page or so back that the panhard bar on my '29 is parallel to both rods of the cross steer setup and the up and down motion is probably not more than an inch. Probably a dead perch has a slightly greater effective length but then don't forget that the spring changes length as it flexes as well, so all in all I think a panhard bar is much better than none at all!

Don Shillady
Retired Scientist/teen rodder