Hello. I was going to do the LS swap but decided against it. I wanted to use an LS-3 for the power but they are just too expensive and I wasn’t going to dump another $10 in the car. For a driver and good power just find a used GTO drivetrain complete with trans . an LS-1 is powerful enough and reasonable. As far as the kit, go with Andrew at jag specialties. HE is a good resource to answer questions and has the gages figured out to work. . 2nd alt is Johns cars. I have dealt with John for 20 years. He knows these cars inside and out. He also has parts. He can supply an LS mounting kit to get the engine in the car but I don’t think he has developed anything else. HE has done mostly LT-1’s and small blocks with carburetors.
Andrew at Jag specialties really has this figured out. If you go with Johns, you will have to spend a lot of time fiddling around. Make sure that you get a ‘complete’ running pullout engine/trans/ Otherwise the conversion becomes difficult.
One key item. Make sure that you have good grounds everywhere with the wiring. It played hell with me on my last conversion. Jag electronics don’t like missing or loose grounds. Everything goes haywire.
It’s a lot of work and its not simple but if you take your time and ask questions it will move along. They hard part is pulling the old engine, cleaning and installing the new one. Once you get past that, its just a lot of fiddling getting it all connected.