I converted my old V8 Discovery from manual to auto - it took me 2 whole days plus a couple of hours on the third day tidying up some of the interior etc, but bear in mind I had never done it before and so was proceeding with caution!
I did have a 4 post ramp though, it would have been a pig of a job without it.
As far as I remember the main bits on the Discovery (would be similar on a Defender Tdi I guess) were
Removal of old manual box
Removal of flywheel and starter ring, fitting of the auto drive plate and starter ring in place of the flywheel
Fitting torque converter to auto box
Fitting stub shaft to rear of auto box
Removal of transfer box from old manual and fitting to auto
Fit auto box and transfer box to vehicle as complete assembly, bolt up TC to drive plate and sort out dipstick tube (which was a PITA as it didn't fit)
Sort out gearbox mountings which were different (supplied from Ashcrofts)
Sort out oil cooler plumbing (my vehicle had an oil cooler on the manual so it was a bit easier, just replumbed this into the auto)
Dismantle throttle cable brackets and replace with new one which has kickdown cable fitted
Sort out wiring for reverse light switch and park/neutral switch
Fit shifter cable to gearbox and route into cab
Fit shifter inside cab and modify interior trim to suit (fiddly job, worse on a Defender!)
Test drive and set up kickdown cable
I got all the bits from Ashcrofts and the whole lot was about £2000 landed here, though a fair bit of that was freight etc, can't recall the exact ex-UK cost. The shifter etc was a horrendous cost to buy new (£280 springs to mind) and I spent a LONG time before I even ordered it going through workshop and parts manuals in minute detail to make sure I had everything I needed - at that stage there wasn't an off the shelf kit available to do the job. It was a few years ago now but I don't think I had forgotten anything when it came to do the job, so it was time well spent

The bit I was dreading - removing the (tight and loctited) flywheel bolts from the rear of the crank proved to be easy as whichever numpty fitted the flywheel when the vehicle was built, forgot to put any loctite on the bolts so they came out quite easily