I have a 95 SE and have had to replace both my 02 sensors on the header and the exhaust. Both were actually easy to do, good old crescent wrench but my only problem was on the install of the lower 02 sensor (exhaust). Apparently the o2 sensor that was installed prior had stripped the thread on the exhaust pipe. Bad thing. At this point I only had 2 options, new exhaust pipe from dealer (about 300-400 hundy) or try and find a fitting at the junkyard. Well one thing I found out was trying to find a 240 in a junkyard is a pretty rare thing. Personally I did not find any240 but Nissan uses the same size threading for all the sensors. So I bought one off an 88 Maxima, and had a shop add threading part to my exhaust. Labor and parts was 45 bucks.
20 for the Exhaust manifold from the Junk, and 25 for labor, ouch. So if you do not have any thread issues you should have no issues. BTY
Intake o2 sensor: 60-65 at the dealer. 30 at the local part store. Dealer parts always recommended.
Exhaust o2 sensor - 80-85 at the dealer. Dealer part only
Hope this helps
Pete 95 SE <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/eh.gif" border="0" valign="absmiddle" alt=':eh:'>