Yes, definately you have to have something to aid you in pouring your oil in, other than just a funnel. I used a $10 hand pump from the local autoparts place with two hoses, one in the bottle of oil, one in the diff...just pumped until it overflowed and then stoped. Another (cheaper) way is to just get some 1/2" tubing, put one end in the diff, then a funnel into the other end. Hold the funnel higher than the fill plug on the diff (otherwise it won't work) and then just pour.
Also, I think the fill plug on the diff is facing backwards just like the drain plug. I'm not sure and I don't feel like checking <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt='
'> but I think it faces back...not to the side like the tranny fill plug.