In the drivers compartment, the only adjustment to be made to the bar locations would be fore and aft on the main hoop for leg room if using stock steering and pedals. Unless the driver is freakishly short or tall, that's pretty much a standard location. Back in the car a bit. The seat doesn't need to be against it. And the next guy to own it might want the seat to go back. The rest of it gets put in as close to the body/headliner/B pillar/ doors as possible to give as much room as possible. This usually takes some planning and effort to get it all welded up 100%. Helps to get the windshield out, Fast Super Stock and other stock body 25.x type deals or cars like a SN95 Mustang often have the roof removed to get it all done.

Frame ties are 2x3x.083, stood on end through the floor. Mopars get the back of it poked into the front of the stock frame rail, maybe half above and half below the floor. Section it up in so it fits up against the torsion bar X member, Outriggers from the frame rail to the rocker, also sectioned into the floor, provide solid mount points for the cage.