well at least you arent bullshitting lol. it looks good though. i think you probably cut a little more out of the floor than you needed to. considering youre only gonna use the back half of the car, i would have kept the front half of the floor intact to make seating etc. easier. if it was my project, id cut the rear portion out and weld the front half of the accord/prelude/whatever in its place, similar to the SHO conversions people do in festivas.

as far as having an aluminum chassis, thats not the best idea. aluminum its WAY softer than steel, so its more likely to flex hard as opposed to steel. at least make everything surrounding the driver out of steel.

and about your weight expectations... it MIGHT weigh close to 500 as it sits, but with a cage, motor/drivetrain, and all the other stuff youre gonna need, its more than likely to end up around 1500. think about it, ~500 for the motor/trans/etc, ~400 for the cage, ~250 for the floorpans/interior bits, ~100 for the fuel cell, lines, etc, ~22 for driver and seat, and ~150 for other random stuff that im too full of turkey to think about... its gonna end up close to 1500 if youre lucky.