A compression test and leak down figures will reveal a lot about the health of the engine - you must get this done. Look for good heat exchangers and exhaust. Does the heat work inside the cabin, for instance, no fumes too. Is the engine leaking oil much? Does it start good from cold and idle smoothly, plus go the the rev range cleanly when warm?
I'm guessing it's a US spec 911T, in which case it shoulf have mechanical fuel injection (MFI) - parts and service can be expensive on MFI, thus starting, running well, etc. is very important.
Get your mechanic to check out the tranny too.
Good luck and love to see some pics of it....
