We just went though a lot of problems on another thread installing the Voyager system on a 350 that previously had TB-IV... It's definitely NOT plug and play... .Quite a lot of wiring changes to be made to get it to work properly (and even then, not as good as the TB-IV)....
There isn't a huge wiring problem, it's just a matter of following directions and paying attention to details. The Merc 3.0L engines have been using the EST distributor since 91.
When the complete EST kit is cheaper than the TB4 module alone, then why not upgrade?