The answer to your question is two fold ... It is posable to do a DET Swap in an Altima , But it is NOT a bolt in , I have been looking at this for the last couple of years and the answer is it would be to time consuming and expensive to be worth it ... If you really want a 4 door SR20DET Car Buy a G20 and swap it , That is a very easy swap ...but The Altima Problems Are as Follows ...... The Altima Trans. will not bolt to a SR20 , and the Sentra SE-R Trans. will not mount to the stock Altima mount location , so that would be custom , The lower mounts would have to be custom ,you will be converting from a Hydraulic activated clutch to a cable clutch , how ?... The Altima ECU and Wiring could be used but you will need a $600 JWT upgrade to make it work , or get the SR20DET ECU and a complete wiring harness ... And there are tons other variables like axles , and accesories ...that also come into play ....... Yes it would be an awesome swap but It just isnt woth the time or effort ...... Sorry
And yes the do build AWD SR20DET's that can be used in a FWD ...The RWD versions will not work at all !!!!