I'm 6'5" and 230 pound with size 14 shoes. I fit fine in my Kirkham with no modifications. If you have a 15 inch steering wheel you will be fine. If you want a little extra room, just get a original style racing bucket.
The 289fia's has the same footbox dimensions as the 427's since the Kirkhams use 427 boxes instead of 289 boxes (289 boxes are bigger).
Hope this helps.
Mike
PS - David, I sent you an email re: fan brackets for mounting my Serck FIA
oil cooler. I need measurements and possibly a pic.