While this is our first post here, I think you may be interested in a product we developed that fits very well with the need to relocate a trolling motor in a linear fashion. While our system isn't useful to just trolling motors, and is actually a linear bearing system, we have catered somewhat to this particular area initially.
Drop by our website at ShuttleSlide
and see if it may be useful to you. I've attached a couple pictures from a recent customer install.
Let us know if we can help. Best of luck to you!