LRBen

Keeping the original gearbox is a decent idea, not sure how an auto box will cope with the motor. I haven't heard of one being used before.

If you are in the UK, I would advise against the MGF as a conversion. The interior dimensions don't lend well to conversion and the DVLA is being a complete pain in the ass. You have to avoid cutting any bodywork or chassis and only use original bolt holes. If they spot something has been cut or drilled you'll need to get an IVA. This is fine for the car but any battery boxes will need certification which is currently costing around £5k.
If you do still want to convert an MGF got for a donor that is pre 2001 tax change. Otherwise you'll still have to pay the original road tax as again the DVLA is refusing to change the tax band of EV conversions post 2001 when the tax is based on Co2 emissions and not engine size.