A Porsche G50 is a very practical choice for the following reasons:
1. Universally available.
2. Parts are easily obtainable.
3. Cost is not unreasonable.
4. Upgrade parts are available.
5. Wide choice of gear sets.
6. Handles good amount of torque.
7. Adapters, clutches, & flywheels are available for many engines.
One thing I think is frequently overlooked in the rush toward ever-increasing amount of horsepower in GT40s and other mid-engine cars is the detrimental effect of vehicle weight. By reducing weight, you've done the same thing for performance as adding horsepower---except that you've now reduced the stress on the transaxle, CV joints, axles, clutch, and stub axles. Yes, you may need to sacrifice a nice stereo system or other amenities but if track performance was your goal you wouldn't use those anyway. I learned a long time ago that one cannot arrive at an acceptable compromise with a "dual-purpose" car. The inevitable result is a race car with marginal performance that is not pleasant to drive on the street. Of course, some are willing to put up with these results and I say, if you are happy with what you have, that's fine. We all make choices.