Dual fuel on an EFI vehicle doesnt show much of a drop in performance over a dedicated LPG system, but on a carby vehicle the benefits are huge to use the EFI manifold and dedicated LPG as the shitty little carby on them was quite a choker.
I'm guessing, by your mention of sensors, that you have an '87+ XF with EST in the kickpanel for spark control?
With any of the LPG systems, it is always better to have a different ignition curve (the point it starts to advance and how quickly it does it), but you can leave it as it is and use the pre programmed ignition curve in the EST.
From memory I dont think any of the sensors, etc are reliant on the carby being there, all you would have to do is relocate the pipe to the MAP sensor onto the new manifold.
Now about the debate about GasResearch stuff....
Yes the IMPCO gear is extremely reliable, and there are plenty of people out there who know what they are doing in terms of repair and tuning, but the mixers work in such a way that makes them no good for performance applications, they tend to run rich at idle and lean at high RPM.
The GasResearch stuff is a little more expensive to set up initially, but you can often find them in the trading post for a reasonable price, The GRA carbs are a fantastic bit of kit, and from all accounts I have heard about them, they end up more economical and give a decent increase in power too.
GRA themselves do seem to charge a bit of a premium for their time and expertise, but when it comes to their gear, I beleive it is worth paying the extra for them to do it. (see thread Disappointed....
for the reason why I recommend GRA only)