I second that. I have an 89' and the stock driveshaft would've worked fine but it got bent somehow. I'm using the JDM driveshaft, really nice has 2 universal joints, came with the clip. You shouldn't have any problems with the drivetrain by using the stock driveshaft. It will line up good, no loss in power and no vibration(unless it was bent like mine but you'll know as soon as you drive, it's horrible). Your motor wouldn't sit any coser to the fire wall, motor mounts make sure the motor stays in the same place everytime. It'll be ok.
As for the AC, yes you need all of the lines from the ac system from a DOHC as well as the compressor. For the power steering you should just need the high pressure hose. The return is just a regular hose easily found at your local auto parts store. If you dont buy a front clip(highly recomend the clip) you will need a DOHC cluster, well actually just the tach. Everything else in your cluster will work just fine. Any other questions about the swap hit up
http://www.nissanperformancemag.com they usually do pretty good write-ups.You'll be fine swapping the motor as long as you have good mechanical skills. Just get a lot of info from several places and compare. Good luck