bear with me and i'll also get back on topic
in the last few decades, since the gas crunch of the 70's, we have let the car manufacturers get away with calling things a sports car that really aren't - this is because they stopped making them - the idea of a sports car flew inthe face of the economically minded bean counters that ran the companies - a homoginization of the sports categories happened and the blurring has not since been corrected - there are many different performance related groups, for example, sports exotic, sport touring, sports coupe, and sports car (often called roadster)
sports car, by definition is for sport - not utility or comfort - things like air conditioning, power windows, power seats, and such are not things to be found in a true sports car - a true sports car would have no frills, be pure perfomance oriented, and be very light - a true sports car is basically a race car with an interior - it should also be 2 seat, convertable, and red, but that's a whole different t-shirt
this is not what a porsche is about, at least not in the last 30 years - they have become a sport touring car - this is a good thing for most drivers - they want the creature comforts that these cars provide, and are generally willing to compromise in performance - that's great - they make a good car for exactly that market
some of us though want more - some want all out sport, and some, like me, want something in the middle - unfortunately porsche doesn't make the stuff we want - that means we have to go elsewhere and transplant or modify things to get the performance that we are looking for
ok - back on track now
having done similar things myself, i agree with dave that any such change is likely to induce exactly the kinds of things he is talking about - in designing the chassis, the manufacturer goes through extensive testing to isolate and control anomolies created by the drivetrain - dropping a different drivetrain in there changes everything - you can expect a lot of new odd things to pop up
none of this makes it wrong or bad to make any change - it's fun - it's not like it's worth anything significant - these cars are cheap - while a nicely built touring car as it stands, they are a good platform for those who want something really special
for those of us who want more, or are used to faster or lighter cars, the car is severely underpowered and way overweight - go for it - play around - enjoy it - most of all, DRIVE IT!