It varies GREATLY depending on how low you want the body, what type of bodydrop (traditional, stock floor, tunnel...), vehicle, size of wheels...
It's not something you either 'know' or 'don't know.'
Every truck is different, in this aspect. You do need a pretty good knowledge of the intricate details of certain systems, though. Last time I cut one up, we had to pie cut the hood for it to close, buy a MUCH smaller brake booster and remount it, hide the heat system up under the dash, change the mounting points and lengths on the pedals...
And put some bucket low back seats in.
Personally, I wouldn't bodydrop a truck unless I was going to the doors.
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PS:
I'm looking into picking up this suburban.