Have been ground running various aircraft/engine types, with several companies, for over 20 years. Basically no special requirements, except being authorised on type and having appropriate simulator training for the task.
At one company I was at in the far east , they did an eye sight test for all authorised engineers. While the staff were sitting in the small waiting room, they memorised the test card that was being used... Eventually it was found out and further tests were carried out using a card with E's, at different angles on. Many required corrective lenses.