Without divulging too much information lest my wife and her friend kill me, I've had four people (3 adults, 1 child) at a total of 540lbs on my pedal car (pictured in the first post of this thread).
Normally this pedal car was designed to be a two-seater -- not a four-seater. This is a pic of the original American Speedster Sidekick model design:
Instead of using the individual boat seats, you can also make your own bench seat like the American Speedster Golf Coaster model:
The Sidekick model (the design/model that I used for the base of my build) uses 1.25" PVC pipe, which is a rather strong pipe size. If you look at the pictures of the bike, it was specifically designed so that there aren't many pieces of pipe that are very long, which minimizes flexing. The bottom rails of the pedal car have chainlink fencing top-rails inside the PVC almost along the entire length. The rear "axle" has a 1" hardwood dowel inside the PVC from side to side. I also put wooden dowels in the PVC holding the seats, and reinforced the boards that the seats are mounted to using 2"x2" boards on the bottom of each plank. Here's a pic showing where the reinforcement is (Yellow is the chainlink fence railing and Green is hardwood dowels):
I am 6'3" myself, so I had to modify the original design a little for my height. You can do this in three ways: (1) Stretch the chassis and/or (2) raise the height of the "dashboard" and steering wheel for leg clearance and/or (3) Raise the seats. I ended up doing all three. You can only stretch the chassis a maximum of about 3 inches without having to fabricate a new crank support shaft. Fabricating a longing shaft wouldn't be terribly difficult -- it's just an aluminum pipe. I also raised up the "dashboard" and to make up for the stretched chassis I lengthened the steering column so I could more easily reach it with my arms in a more relaxed position. Because I used an alternate step through side design, the seat mounts ended up being about 1" higher than the original design which helped a little for my height issues. I'm very happy with the results and I'm perfectly comfortable pedaling and steering with this modifications.
So, long story made short (too late!), yes, I think this pedal car could easily accommodate your weight and height. The design is really easy to modify during the build, because you cut everything, assemble it, and then take it all apart and glue it. Prior to the disassembly and glue, you can easily make what changes you want/need. I planned some of my modifications ahead of time, but also made quite a few changes on the fly when I saw potential problems/issues.
If you attempt this, good luck and have fun! I certainly had a lot of fun building it and equal amount of fun riding it around now.
-- Chris