First backup your stuff ! 

Installation 
- Common files : Copy the content of Heidi Express into your Railworks folder

Optional 1 : Lower max speed to 65 Km/h : Copy the content Heidi Express speed track into your Railworks folder

Optional 2 : LGVmed platform character (LGVMedSouth required) : Copy the content Heidi Express LGVmed into your Railworks folder

Note : 
Kuju.ap content some characters from Railsimulator and RailsimulatorUS which are provided with the Heidi Express in a sub folder of UMC. 
You don't need kuju.ap if you have EU and US assets packs. 