Anybody here familiar with getting a heavily modified car to pass Shaken? (車検)

I'm going to start work on a pretty extreme new build this year, (engine swap, cantilevered suspension, tubular front end, full replacement body etc...) and I want to know what I have to do in order to keep it street legal since it wont pass a normal Shaken, but I know that there are different regulations / requirements for modified cars as long as you register it and submit to the inspections.

I've spoken with quite a few of my mates with custom cars around Chiba / Nagoya and they mentioned something about having to get their cars to pass engineering specifications and be reclassified. My friend with a 1.9m wide Rx7 mentioned he had to do something called a "width change registration" or something for his widebody but the information they give me is pretty patchy.

I'm just finding it super hard to find the information on all this on what's allowed and what's not. Obviously googling it just tells me all your standard Shaken checklist things for your normal everyday vehicles, but I know that getting modified cars to pass is a slightly different process I just cant find anything on it.

I just moved to my new house in Chiba a few months ago from New Zealand and back there we had a "LVVTA Car Construction Handbook" which was basically a rule book on all modifications you were allowed to do as long as you got them certified. Just trying to find the version of this for Japan's Shaken.

My Japanese is pretty limited outside of day to day conversations so I don't know the words for a lot of what I'd be looking for.

Any help would be appreciated.
Cheers