e.g.
www.paddockspares.com do pistons with rings for 66 dollars each......inlet valve for 8 dollars etc etc ..all plus shipping.
Fitting a Discovery 200tdi to a LHD Defender can be done with only a few bits needing fabrication...or you can buy all that's needed from
www.steveparker.co.uk. I have a 300tdi turbo and inlet manifold fitted on my 200tdi to allow this...easily found second hand.
What I find is that older Defenders can be bought here in Europe at OK money for what they are I guess.Have a look at
www.leboncoin.com and see what's what. A reasonable LHD plus 25yrs old Defender here will set you back about 7500 dollars upwards...cheaper still in Spain due to the economic crisis there.(I spied a utility 300tdi 5 door station wagon 110 with 400k kms last week going for 3500 dollars...but too young for the US) A rough Defender needing the crap Turbo Diesel from old replaced/or with a seized motor can be bought from 2000 dollars. Here the chassis(if sourced from Southern France) will be relatively rust free compared to the north where they use salt on the roads in winter.
Try
www.ebay.co.uk .co.uk and
www.autotrader.co.uk to see relative prices for Defenders (and how much IMO you're getting fleeced for)...albeit RHD ones..another site for LHD is
www.mobile.de