After re-reading your post, only a few months to go? Spend that few months doing more research, even buying parts that you might want to modify your GTT with etc... I'm sure that all would agree that it will be worth your wait to legally get a GTT to begin with rather than stuffing around with all this motor swapping, that and 2xmotor swaps will set you back around 2.5k.
If you want to build the motor though, perhaps buy the GTT now, and spend those few months building the motor to have it rady in time for being able to drive it. These things take time to research, buy, carry out the labour, then tuning, then re-tuning after running in the built motor. If you have a parent that can even drive the GTT for the run-in period after building the motor, it will be all the more fun once you have it good to go and off your provisionals.