I am in the process of doing exactly the opposite. V8 on LPG with 4 speed auto to 300tdi manual. I have just put an offer in on a full engine through to transfer box with the radiator group.
So out of mine will be coming a complete plumbed 3.5 EFi on carbs with a ZF auto along with a one year old radiator. Got all the EFi valley as well bar the mass meter, also the full wiring loom, ECU and exhaust system. The simple LPG systems are easy to wire you don't need all the sensors as the brain can work things out as long as you have the Lambda sensor in the downpipe.
I love the V8 / auto setup, makes driving in town so easy. The main reason for the change is the range and availability of LPG. We want to go to the far reaches of Scotland and I don't want to be continually searching for LPG. Yeah you can plan around LPG stations at 50 miles apart, but there is no guarantee that they still sell the product and we like to take a diversion on a whim.
Hope this helps