thats an issue which will surface after sometime.
A toyota, nissan or honda, u can get literally every thing related to maintainance and engine builds. you even get the torque numbers for bolts.
Saga engines u can get some FSMs (factory serive manuals) and maintainance manuals,
other chineses engine manuals and FSMs are nearly impossible to get. (MG uses Shanghai GM engines and some of their engines have been in chevorlet sedans, u can get some details about them from chevorlet forums)
The bigger problem wont be engine rebuilds/maintainance though, it would be other maintainance jobs like throttle body, engine sensors etc, stuff like that.
I have seen people claimaing k china agar toyota k spare parts banata hai to chinese gari k bhe banaye ga. Not necesserily. Any 3rd party will make spares/ copy spares if their market is big otherwise there is no point making them as they would cost more than company ones.