Hey
was this a 4wd or 2wd model?
I just did an engine swap on a 4wd td27 diesel.
With the 4wd model you need to move the gearbox backward, or remove the front diff so you can move the engine forward (sump is very close to diff).
I had to replace the diff anyway, so i dropped the front diff and left the gearbox. Overall the engine change was pretty standard.
Undo bolts, unplug everything, drain everything, remove radiator, pull out engine... etc.
Removing the front diff on a D21 can be a PITA or it can be very easy, depending how you go about it.
The first time we did it the manual advised to remove rear brace, undo bolts, lift engine up and mounever diff out. This is possible, but there was a crap load of swearing etc and much time spent getting everything into the exact position so the diff would come out (oh and lots of hitting things).
I don't do it that way anymore. The main reason the manual says to do it this way is there is 2 (top) bolts that cant be undone on the main diff cross member without removing the torsion bars (d22 is different, these are easily undone on a d22, just d21 has suspension components in the way)
So what you do, is get a small handsaw or die grinder or whatever you have and cut the head of the bolts. This way you can drop the main diff cross member and not worry about lifting engine or any other headaches. Then you simply replace these bolts with shorter versions and put the Nut on the side the old bolt head was on. This makes for easy future removal to.
so the general instructions for removing the front diff would be :
Undo Cv's, then cable tie them up out of the way. (6 12mm bolts either side)
Undo front drive shaft, cable tie out of way. (4 14mm nuts/bolts i think)
Undo 3 nuts on top of diff housing. The bolts go through the rear cross member and hold the diff in-place.
Undo breather line
undo two bolts holding metal breather line to main cross member
bend metal line out of the way
On the main crossmember there is 4 bolts.
Undo the lower two, and remove nuts and push bolts flat so they are still holding the cross member in place.
remove the top bolts / cut them off.
Undo the two side bolts holding in the rear cross member.
Lift diff up (using hands, its still held in place in) mounever rear cross member out.
support main cross member with a jack or something.
Remove the last two bolts you left just sitting in main cross member.
now nothing is holding it in.
I find the diff will hold itself there, so i remove jack, put a spare tyre underneath it and hit it from the top with a crowbar or something till it falls into the Tyre.
Of cause you may wish to do it another way, but this is just what works best for me.
there is a couple of pictures here
http://www.navara.asia/showthread.php?t=7258&page=3
christian