I'm genuinely not trying to burst your bubble. or denture you from building this out...I think it could be sweet!
But.....
Let's say you figure out how to go 3 wide. "Typical" suspension seats are nearly 24" wide OA.. 3 seats are too wide for a row. Interior width is
68 " How deep do the "door" seats have to be behind the center seat to fit the door frame? Are you going to extend the cab? Chopping the xhit out of the door frame? You mentioned a cage too.. There are a couple fellas at Chuck's that have wider shoulders Measure their shoulder width at lunch time...
You will likely have to straddle the powertrain( and steering linkage) in some aspect,. Brake on the left, throttle on the right? Mid-engine, V-drive, etc..when you get there.. Are you comfortable with your passenger(s) having direct access to your peddles over your feet? You plan on making power. Big power Power that will make you expecting passenger scared. Your right passenger panics and make you go WFO as they slam on your foot. You can't do a f*ckin' thing about it...
Hold on..