I was looking into these, they command a fair amoung of cash as they are the last RWD air cooled porker turbos. There IS the 993 GT2 but thats gonna be a whole different ball game.

When looking around 30 oddk gets a 3.3 turbo which is 320 brake and you can get around 380 before you need to spend mega bucks.

they did a 3.6 turbo as well 360 odd brake IIRC (the 3.6 lump wasn't ready in time for the original 964 turbo so they used the 930 one with a few tweeks)

The 3.6 came with the "big reds" and a RS rearbumper tand a few other tweeks they didnt make many before the 993 turbo was out so they command a bit more 36-40+ when I was looking.

the 3.6 is one to keep standard IMHO as any mods will probably devalue it.

they did a turbo 'S' as well which is even more, but the same performance.

There was never a 965 this was an abandoned project by porsche and some of the part numbers on the 964 have the 965 number which confuses people. (or they call the 3.6 the 965)