The Jag IRS in my '49 sits about 2" under the bed wood. With the half-shafts level the running boards are about a beer can off the pavement, which is the normal way my truck rides ( this Jag IRS has been narrowed about 3", so it has Corvette-style half shafts.
The center section is a 'drop out' with removal of two pins at the end of the ladder support
If you want to see more details of the IRS installation in my '49, check out my build thread
https://67-72chevytrucks.com/vboard/...=725080&page=9