Modding / Replacing files / Problem (Grand Theft Auto 5)

Need help from a person involved in modding or those who are well versed in the game files. (Sorry for the wording)
Replaced the Elegy on the Elegy Retro, but there are problems.
The speedometer and other instruments are no arrow
Tuning is not installed. Just tried to replace the file from Retro, to rename the files within it (with elegy1_* on elegy_*), but the game or crashes, or sees the standard tuning of the Elegy.
You need to add a new tuning and to adjust its position. Fixed position in the file *_mods or need to replace from other text files?
In General, if someone can help - waiting for you