Need help to identify an Enfield No4 MKI

[Dampherb]

So its probably have been rebuilt from unknown parts and made by BSA even though the owner claim its an original Maltby.

But what does the ''G'' in the serial number mean ?
Do you think its a great purchase for hunting and fun shooting or it might be a risk considering I don't know where the other parts came from ?

And if it is a BSA rifle, why does the serial start with a 1 ?