Hello and welcome!
The VIN numbers can be a challenge. It can depend on the type of car your MG replica was built on. With Fords the VIN was on the dash or the door frame, so good luck with that since those are gone. With VWs the VINs were on the dash, under the hood, or on the tranny hump under the back seat. Again, good luck. With Chevettes they sometimes had the VIN on the dash, door frame, or if lucky, on the passenger side of the tranny. You don’t say what type running gear, so your best bet may be the previous owners registration. In my case the car was registered from the factory with a VIN from a ’84 Nissan. Go figure! Anyway, if you want to know about parts for the engine or drive train, then there are usually ID numbers on the engine block that you can use to determine year, options, etc.
Again, good luck with the original VIN of the donor car.