The Defender restoration community is full of thieves, shysters and con-men with a sprinkling of honest businesses. Research the crap out of whomever you do use and in most cases you get what you pay for. Additionally it is very tough getting a diesel CARB certified. Because somebody says they can do it and actually getting it done is two very different things.
Lastly I would find a 300Tdi 110 with and automatic and take it for a test drive. When I drove one I thought it was an absolute underpowered dog compared to mine with a manual 5 speed.