Ironically it is not a problem that can be solved by yet another software system to learn and use properly. The mess you and many others have found is symptoma

Ironically it is not a problem that can be solved by yet another software system to learn and use properly. The mess you and many others have found is symptomatic of a lack of cohesion, standards and conventions. It is just too hard to retrospectively sort out such a mess. When everybody is hard at work on current projects, where is the time going to come from to clean up the past mess? The only feasible solution is to implement a clean new system for all work from some point in time. Of course, it requires management fortitude and staff buy-in -- neither being easy but absolutely essential. The most viable approach for you is to do an absolutely stellar job with your current client. Then using them as a reference site approach comparable firms with your proposal to fix their pain point. That is where your configurable PLM comes into play. But you will need to do all the work. Clients will not buy such software and then invest in yet more time and effort (i.e. money) to learn it well enough to configure it for their needs.