Sorry, that's must be my English, but I can't get to your point. Did you tried to read about that guy with his santa fe car? I only have chosen him because it is a 6cyl car recorded experience with successful conversion to LPG with complete DiY that google translate can do a decent translation on. The guy who did the conversion is an engineer working for Hyundai in Russia. The guy seems like he has enough income to afford a professional conversion, but he deliberately chosen the hardest (on your opinion) way to do it. Working only weekends he did full conversion of his car DiY.
Google translate Google translate refers to LPG like HBO for some reason, but the point is clear. About software you need to read the second part of his writeup. Before that 4 years ago he converted his Hyundai sonata from Necam like system to the 4th generation using stag kits. That is an interesting read because he is really slow there. He slowly getting to the point why and how he decided to abandon older system and start all over again with only front kit. 4years running without any issues is an achievement and I highly recommend to read it. If you are interested into understanding why and how its can be done diy.
It seems that the hardest part of the conversion - fuel management is can be done now using software automatically(yes anyone can download it for free). I don't want to underestimate the job that ClassicSwede or others installers doing, but it seems that the only hard part left is to choose the right kit for your car that can be done only by experienced installer. Installation done diy will be still illegal as by UK law can only a certified installer convert a vehicle to alternative fuel.
In my personal opinion installing the LPG nowadays is like installing a dishwasher . Someone is capable to do it, someone not and someone is capable but don't want to get his hands wet.
Again only judging from my personal point of view installing a front kit of 4th generation LPG is easier than changing wishbones or shock absorbers.