Hopefully someone will have better information and you have not stated if this is a flying engine or ground running. Even when I worked on the 601's (HS125-600) I don't remember having any documentation for going into the engine in any depth. As they were nearly all "Power by The Hour" any internal work involved exchanging the engine.
You might even have problems getting a manual from RR!
Best I could suggest is contacting a present Hawker 126-600 Operator of which there are very very few left, ebay, or one of the companies parting out the aircraft. Even an Aviation Museum? Some historic Jet Provosts are still flying in the UK but with a different model of Viper, the Mk202, however, they would certainly have some heavy maintenance manuals. Plus the Jet provost owners may have knowledge of workshops.
Sorry not much help
M.E