Carerra to GTS/GT3 RS conversion useful?

Hello, I now play with the idea of getting a 991er. From the type I like the GTS and the GT3(RS). But because I can’t agree with my conscience 150k and I don’t necessarily have to drive a new car, I just thought of buying an older model as a base and then “doing” it direction of my dream setup. As a base I imagined the Carrera 996 or 997. Does there basically something against it? Someone has a clue what to do with the conversion. I would be very grateful for comments, experiences.