Not sure if I've messed up somewhere along the line, but the install instructions for the new Scripthook were :
Installation:
1. Copy ScriptHookV.dll to the game's main folder, i.e. where GTA5.exe
is located.
2. In order to load asi plugins you need to have asi loader installed,
you can download it separately or use the latest version that comes
with this distrib (dinput8.dll).
You must delete old dsound.dll asiloader if you have one installed.
3. This distrib also includes a sample asi plugin - native trainer,
if you need a trainer then copy NativeTrainer.asi as well.
After completing these steps, the game wouldn't load so I grabbed the dinput.dll file from the address I posted and now it's running. Apologies if I've given some incorrect advice but it appears to be working for me at the moment