Consider using 2 horizontal plates to the 2 engines plus the 2 mid shaft bearings plus the 2 synchro bearings together. One plate will be located above the engines and the other below. Both plates will have a 25-degree brake or 25-degree arc along their X-axis. The lower plate might serve as the cover for the synchro box. The plates will attach to the engines via the boltholes used to attach the conventional factory belt reduction and also the boltholes at the other side of the engine, which attached the pull-starter.