The workshop manual will explain how to set the gearbox up, but will refer parts of the setup to be done with special Haflinger tooling / jigs. This will make it difficult for most mechanics whether home mechanics or qualified mechanics. The dimensions for most of the special jigs are in the workshop manual, so I would be possible to get them made locally.
There are several people / places in Europe and even in America that profess to be able to do work on Haflingers. I realise these are not likely to be viable options for the OP.
There was an official importer for Haflingers into South Africa, maybe if you could track down the place where the company was, there might still be someone who provide some more information on the service system that existed and from that possibly information leading to someone with the knowledge to do the required repairs.